Welcome to 3rd form Physics. This page will contain invaluable information which will help you through the year. Make sure that you bookmark it!

3H 13/12/?

HW Revise for a test on all of electronics in the first lesson of next term!

3H 13/12/5

We did some GCSE electricity questions just to show how depressingly easy they all are.....

We'll just make sure of adding parallel resistors on Thursday.

3B 13/12/5

We also made a circuit which acted as an electronic thermometer. This was achieved by putting a thermistor in series with a fixed resistor. As the temperature rose, the resistance of the thermistor fell, this meant that the share of the battery voltage taken by the thermistor also fell. The voltage across the fixed resistor therefore increased as the temperature rose. We used ice and boiling water to calibrate the device.

An LDR (light dependent resistor) could be used in place of the thermistor to make a light meter.

HW Revise for a test on all electricity in the first lesson of next term.

3B 09/12/5

RM was absent last lesson. We went through the electicity test answers and then looked at adding up the resistance of several resistors in series and in parallel.

Resistors in Series

Simply add them up!

R₁ + R₂ = R_Total

Resistors in parallel

1/R₁ + 1/R₂ = 1/R_total

This is a little harder, as you have to be able to do some maths. Here is an example:

A 3 Ohm resistor is put in parallel with a 12 Ohm resistor, what is the total resitance?

1/R₁ + 1/R₂ = 1/R_total

So 1/3 + 1/12 = 1/R_total

1/3 = 4/12

4/12 + 1/12 = 1/R_total

= 5/12

Cross multiplying gives: R_total = 12/5 = 2.4 Ohms

Your answer will always be somewhat smaller than either of the 2 resistances in parallel.

Books were taken in to mark cover work. 3 commendations for a correct solving of the cube of resistors problem!

3H 08/12/5

RM was absent last lesson. We went through the electicity test answers and then looked at adding up the resistance of several resistors in series and in parallel.

Resistors in Series

Simply add them up!

R₁ + R₂ = R_Total

Resistors in parallel

1/R₁ + 1/R₂ = 1/R_total

This is a little harder, as you have to be able to do some maths. Here is an example:

A 3 Ohm resistor is put in parallel with a 12 Ohm resistor, what is the total resitance?

1/R₁ + 1/R₂ = 1/R_total

So 1/3 + 1/12 = 1/R_total

1/3 = 4/12

4/12 + 1/12 = 1/R_total

= 5/12

Cross multiplying gives: R_total = 12/5 = 2.4 Ohms

Your answer will always be somewhat smaller than either of the 2 resistances in parallel.

HW Try at least question 1 of the adding resistance handout.

3B 02/12/5

We sat the short energy test.

We also went through the electricity test.

3H 01/12/5

We sat the short energy test.

We also made a circuit which acted as an electronic thermometer. This was achieved by putting a thermistor in series with a fixed resistor. As the temperature rose, the resistance of the thermistor fell, this meant that the share of the battery voltage taken by the thermistor also fell. The voltage across the fixed resistor therefore increased as the temperature rose. We used ice and boiling water to calibrate the device.

HW Design a circuit that could be used as a light meter (like a cricket umpires') and explain how it works in your book.

3H 29/11/5

We also sat the test (elec. only)

HW Energy revision.

3B 29/11/5

We sat the electricity test (but not the energy 'cos I forgot it.)

We tested the resistance of a component called a thermistor.

Resistance is calculated by using Ohm's law:

Resistance = Voltage / Current

The resistance of a thermistor varies with temperature

It is the opposite of a light bulb, the resistance falls as it heats up. This is because the thermistor gains extra free charge carriers when the temperature rises, making it a better conductor of electricity.

HW Just look at energy so we can sit the bit of the test I forgot!

3B 25/11/5

We looked at some GCSE calculations using Ohm's law. You can work out the resistance of any component by:

Resistance = Voltage / Current or R = V / I

If there are 2 components in series, you must add their resistances to get the total amount of resistance in the circuit.

Ohm's law can be rearranged to find the voltage or the current if they are unknown. A quick, cheap and cheerful way to do this is to write out the following triangle:

Cover up the unknown quantity to reveal the correct formula.

HW Revise for a test on energy and electricity.

3H 24/11/5

We tested the voltage/current characteristics of a diode. We tried to push current through it in both directions.

A diode only allows current to flow in one direction. Backwards only a very small current indeed (practically zero) will ever flow. Its resistance in a forward direction roughly obeys Ohm's law (if you double the voltage, the current will also double).

We also tested the resistance of a component called a thermistor.

Resistance is calculated by using Ohm's law:

Resistance = Voltage / Current

The resistance of a thermistor varies with temperature

It is the opposite of a light bulb, the resistance falls as it heats up. This is because the thermistor gains extra free charge carriers when the temperature rises, making it a better conductor of electricity.

HW Revise for a test on electricity and energy.

3H 22/11/5

We discussed the shape of your voltage/current graph for a light bulb.

A light bulb does not obey Ohm's law, current and voltage are not proportional.

This link brings you to an excel file with a set of results for a light bulb and a graph.

The resistance of a light bulb increases as it gets hotter. The particles in the metal vibrate more as they get hotter, causing more collisions with electrons trying to pass through the material - hence the resistance increases.

3B 22/11/5

We did some more experiments looking at how the voltage across a component varies the current through it. This time, we tested a light bulb and a diode.

HW Finish both graphs and answer the questions below.

Questions about the light bulb graph:

1. Describe in words how the gradient of the graph varies.

2. What does this mean about the resistance of the bulb?

3. What physical reason can you think of for this?

Questions about the LED graph:

1. Describe in words how the gradient of the graph varies.

2. What is the resistance of the LED when connected backwards?

3. Does it obey Ohm's law when connected forwards? (explain you answer).

3B 18/11/5

RM absent at CCF, cover work.

3H 17/11/5

We had a lesson in which you built and tested a circuit that can be used to see how the current and voltage across an electrical component vary in comparison to each other.

(We plotted the graph the other way round, with voltage on the y axis)

You found that voltage and current were proportional for both the components we tested. These components obey Ohms law: Current is proportional to voltage, the constant of proportionality is called resistance.

Resistance = Voltage / Current

The resistance of a component tells you how difficult it is to force current through it.

You also tested a light bulb in the same circuit and found that it didn't appear to obey Phm's law however.

HW Finish off the graphs of your results and answer the questions from the handout explaining the meaning of the gradient of the graph.

3H 15/11/5

We did a quick quiz on the principles of electricity we have learned so far.

Mainly: The current is the same at all points in a series circuit, the voltage across each component in a series circuit will add up to the battery voltage.

and: The current in each path of a parallel circuit adds up to the total current flowing in the circuit, the voltage across each parallel path is equal to the battery voltage.

We then just started to prepare for the experiment we will do next week.

Books were taken in.

3B 15/11/5

You built and tested a circuit that can be used to see how the current and voltage across an electrical component vary in comparison to each other.

(We plotted the graph the other way round, with voltage on the y axis)

You found that voltage and current were proportional for both the components we tested. These components obey Ohms law: Current is proportional to voltage, the constant of proportionality is called resistance.

Resistance = Voltage / Current

The resistance of a component tells you how difficult it is to force current through it.

HW Finish off the graphs of your results and answer Q1 from the handout explaining the meaning of the gradient of the graph.

3B 11/11/5

RM absent. You did Spectrum Phys. qs 1-7 P21/22 and P111-113 on cells. More on voltage and bits next time.

3H 10/11/5

We started to study electrical voltage. The battery in a circuit provides an electrical force pushing the electrons around the circuit. The more energy given to the electrons by the battery, the bigger the voltage of the battery.

All the energy given to the electrons by the battery is used up by the components in the circuit. The amount of energy used up per Coulomb of charge passing through a component is known as the potential difference across the component (but is really just the voltage across the component.)

Wires do not require much energy to push a current through them as they have a very low resistance. Therefore the voltage across a wire in a circuit with other components in it can be taken as zero. Only the proper components (like bulbs, resistors etc. actually use up the batteries voltage.

We did an experiment involving inserting 2 different types of metal into lemons. Surprisingly, we found a voltage was generated across the 2 pieces of metal, we had manufactured an electric cell.

Chemical reactions inside cells are only able to continue when the 2 electrodes are connected together as part of a complete circuit. One electrode gains electrons due to the reaction and becomes negative, the other loses electrons to the reaction and becomes positive.

All commercial cells and batteries are based on the same principle, high voltages are achieved by putting several cells in series.

We found that the maximum cell voltage could be made when 2 metals of disparate chemical reactivity were stuck into the lemon (e.g. magnesium and copper)

HW Qs 4-7 P22, and Qs 4-7 P??? in Spectrum Phyics. Books in next time.

3B 8/11/5

Lots of people on prize day practise. We did an experiment involving inserting 2 different types of metal into lemons. Surprisingly, we found a voltage was generated across the 2 pieces of metal, we had manufactured an electric cell.

Chemical reactions inside cells are only able to continue when the 2 electrodes are connected together as part of a complete circuit. One electrode gains electrons due to the reaction and becomes negative, the other loses electrons to the reaction and becomes positive.

All commercial cells and batteries are based on the same principle, high voltages are achieved by putting several cells in series.

We found that the maximum cell voltage could be made when 2 metals of disparate chemical reactivity were stuck into the lemon (e.g. magnesium and copper)

HW None.

3B 4/11/5

We started to study electrical voltage. The battery in a circuit provides an electrical force pushing the electrons around the circuit. The more energy given to the electrons by the battery, the bigger the voltage of the battery.

All the energy given to the electrons by the battery is used up by the components in the circuit. The amount of energy used up per Coulomb of charge passing through a component is known as the potential difference across the component (but is really just the voltage across the component.)

Wires do not require much energy to push a current through them as they have a very low resistance. Therefore the voltage across a wire in a circuit with other components in it can be taken as zero. Only the proper components (like bulbs, resistors etc. actually use up the batteries voltage.

HW None, books in.

3H 3/11/5

Half term work was returned. Some more personal views about the future of energy production would have been apreciated.

We started the electricity topic.

Electric current is a word describing moving electrical charges. It is the rate of flow of electrical charge. The unit which is used to measure charge is called the Coulomb. (The numbers of individual electrons moving would be very large indeed.)

Current is therefore measured in Coulombs per second. Another word for 1 Coulomb per second is an Ampere

. Electrical conductors are materials that allow the passage of electric current. In order to do this they must have charge carriers (usually electrons) which are free to move.

Metals have free electrons as part of their structure which can conduct electricity.

Although electrons move slowly through metal wires, each electron repels its neighbour causing a knock on effect which means that electrical energy is transferred at the speed of light.

The dissolved ions in a solution are also free charge carriers and so can be used to conduct electricity.

We tested some simple circuits with light bulbs in and came up with the following rules:

1. The current in a series circuit is the same at all points.

2. The bulbs lit up at less than normal brightness in series; less current was flowing through them than in a single bulb.

1. The total current in a series circuit is equal to the sum of the currents in each parallel path.

2. The bulbs in parallel lit up at normal brightness; they had the same current flowing through each of them as flows through a single bulb.

HW Finish Qs 1-11 (in full sentences)from Spectrum Physics pages 18-20 and Qs 1-3 from P21

3H 1/11/5

We got the efficiency apparatus to work. The electric motor lifted up a mass giving it gravitational potential energy (GPE). A joulemeter measured the electrical energy put into the system, and we calculated the useful GPE got out.

Efficiency = Useful energy out/Total energy in

The efficiency of the machine increased as it lifted heavier masses.

The half term HW was taken in, must be sorted asap by non-doers.

3B 1/11/5

We started the electricity topic.

Electric current is a word describing moving electrical charges. It is the rate of flow of electrical charge. The unit which is used to measure charge is called the Coulomb. (The numbers of individual electrons moving would be very large indeed.)

Current is therefore measured in Coulombs per second. Another word for 1 Coulomb per second is an Ampere

. Electrical conductors are materials that allow the passage of electric current. In order to do this they must have charge carriers (usually electrons) which are free to move.

Metals have free electrons as part of their structure which can conduct electricity.

Although electrons move slowly through metal wires, each electron repels its neighbour causing a knock on effect which means that electrical energy is transferred at the speed of light.

The dissolved ions in a solution are also free charge carriers and so can be used to conduct electricity.

We tested some simple circuits with light bulbs in and came up with the following rules:

1. The current in a series circuit is the same at all points.

2. The bulbs lit up at less than normal brightness in series; less current was flowing through them than in a single bulb.

1. The total current in a series circuit is equal to the sum of the currents in each parallel path.

2. The bulbs in parallel lit up at normal brightness; they had the same current flowing through each of them as flows through a single bulb.

HW Finish Qs 1-11 (in full sentences)from Spectrum Physics pages 18-20.

3B 21/10/5

We did some very silly calculations based on the amount of energy in a Mars bar. We worked out the height you could climb to, (about 1.9km!) or the speed you could reach (roughly 192.7m/s!) if you were 100% efficient at converting the Mars Bar into useful energy.

We looked at a little video showing about intended plans to build a new experimental fusion reactor, ITER. It is the single most important scientific project being undertaken by humanity at the present time, so obviously it has been held up by idiot bureaucrats for about 15 years who can't agree where to build it. Look here for more details.

HW None, books were taken in. Except Amaam and Theo who are catching up some missed work over the half term.

3H 20/10/5

Some bookwork on energy resources was completed. We looked at the chain of energy transfers which links fossil fuel and most renewable energy resources to the Sun.

We began to look at the idea of efficiency, but the Joulemeter played up. We'll deal with this next time.

We looked at a little video showing about intended plans to build a new experimental fusion reactor, ITER. It is the single most important scientific project being undertaken by humanity at the present time, so obviously it has been held up by idiot bureaucrats for about 15 years who can't agree where to build it. Look here for more details.

HW Do a mini project on the possible future energy uses of the human race. Include some of the different options available as fossil fuels run out and what, in your opinion is the most likely answer to the expected energy crisis.

3H 18/10/5

We watched a video on energy resources. Fossil fuels are concentrated stores of chemical energy which have form from dead animal and plant matter within the Earth's crust over millions of years. They will run out relatively soon and are generally polluting when burned.

Renewable energy such as wind, wave, tidal, hydroelectric and geothermal is ideal. Unfortunately it costs a bomb to produce and so is not likely to find favour anytime soon.

Nuclear fission is used in some power stations but is also fairly expensive and produces long term radioactive waste storage problems.

Nuclear fusion is the reaction which powers the Sun itself. It does not produce any radioactive waste to worry about and has almost inexhaustible fuel supply. The human race must make this work on Earth within the next 200 years or so to avoid a serious energy crisis.

HW None again, you will be set a task over the half term therefore.

3B 18/10/5

More bookwork on energy. You must be able to trace the energy transfers for most forms of electricity generation right back to the Sun.

We also looked at the idea of efficiency. The efficiency of any energy transfer is defined as the proportion of useful energy out, compared to the total energy put in.

Efficiency = Useful energy out / Total energy in

This can be expressed as a percentage by multiplying by 100.

We performed an experiment to show how the effisiency of an electrical motor lifting a mass varied with different masses lifted.

The useful energy out was the gravitational potential energy (GPE) gained by the mass.

GPE = Mass * gravitational field strength * height

The efficiency got higher when the machine was lifting larger masses. We thought that this was due to it turning slower in this case, so less sound and heat energy were being created.

HW Finsh off Qs 1-11 from Spectrum Phys. P8+9 on renewable energy sources.

3B 14/10/5

Practically all the energy resources which the human race has are based upon originate with our Sun.

We watched a film on energy resources. Fossil fuels are concentrated stores of chemical energy which have form from dead animal and plant matter within the Earth's crust over millions of years. They will run out relatively soon and are generally polluting when burned.

Renewable energy such as wind, wave, tidal, hydroelectric and geothermal is ideal. Unfortunately it costs a bomb to produce and so is not likely to find favour anytime soon.

Nuclear fission is used in some power stations but is also fairly expensive and produces long term radioactive waste storage problems.

Nuclear fusion is the reaction which powers the Sun itself. It does not produce any radioactive waste to worry about and has almost inexhaustible fuel supply. The human race must make this work on Earth within the next 200 years or so to avoid a serious energy crisis.

3H 13/10/5

No-one was here! Quite literally to start off with as you were all being told not to smoke. Then just Yom Kippur people missing.

We went through the forces and motion test, in general it was done well.

We started to discuss energy. Energy comes in many different forms and when it changes from one form to another "things" happen. All physical changes in the universe are associated with an energy transfer.

HW None - not enough people.

3H 11/10/5

We sat the forces and motion test.

3B 07/10/5

We went through the forces and motion test. Mostly fine except for those few who ducked in under 50%. There will be a retest to be announced next lesson.

We then looked at energy. We talked about energy "the capacity for things to happen". When energy changes from one type into another type, then "things" happen. There are several different types of energy: kinetic energy (movement), gravitational potential energy, heat energy, sound energy, light energy, chemical potential energy, elastic potential energy, nuclear energy, electrostatic potential energy etc.

HW Finish Spectrum Phys P1+2 Qs 1-7 and complete P5+6 Qs 1-4 (read pages first)

3B 07/10/5

We sat the forces and motion test.

HW - relax.

3H 06/10/5

We spent all lesson firstly going through the ttt homework in detail, and then attempting practice test type questions.

Most recent HW was not marked - books have to come in at the same time as the test.

HW There will be a test in the next single lesson which will be on everything we have covered so far. Revise!

3H 04/10/5

Horizontal and vertical motion are entirely seperate. We talked about the monkey and the hunter example. If the monkey lets go as the hunter fires at it it is doomed.(whatever angle the gun is fired at the monkey from).

HW I have 2 to mark!

3B 04/10/5

We spent all lesson firstly going through the homework in detail, and then attempting practice test type questions.

HW Revise for a forces and motion test next lesson. That includes those boys missing for a religious festival, we'll see if you check the website!

Here is a past test for you to practise with if you missed the lesson.

3B 30/9/5

We looked at graphs which can be used to represent motion. Distance/time, speed/time and acceleration/time are all related graphs.

The gradient of a distance/time graph gives you the values to use on a speed/time graph.

Similarly, the gradient of a speed/time graph gives you the values to use in an acceleration/time graph.

Motion graphs are discussed here

TTT free fall HWs were taken in.

3H 29/9/5

Single lesson didn't happen, so I took in ttt HW sheet.

We looked at graphs which can be used to represent motion. Distance/time, speed/time and acceleration/time are all related graphs.

The gradient of a distance/time graph gives you the values to use on a speed/time graph.

Similarly, the gradient of a speed/time graph gives you the values to use in an acceleration/time graph.

Motion graphs are discussed here

We did another calculation of the acceleration due to gravity using the timer ball.

We then went on to discuss free fall. Without air resistance, all objects fall at the same rate with an acceleration of about 10m/s/s (on Earth). However, air resistance changes the way that some objects fall.

We looked at drag forces.

Our example was ball bearings falling through a thick and viscous fluid. The large amount of drag allowed us to see the effect on the rate that they fell.

A speed/time graph of thye motion would look like this:

In air, (unless the object is very light), much higher speeds need to be reached.

The above shows how a parachutist first accelerates until the air resistance force on him is equal to his weight. He then travels at terminal velocity, a constant speed with balanced forces acting on him. He then artificially increases his air resistance by opening his parachute, so he slows down until air resistance once again equals his weight at a much slower (and safer) speed.

Terminal velocity occurs when the air resistance (sometimes called "drag") force equals the weight iof the falling object. This means that:

the object is falling with a constant velocity - its acceleration is zero.

heavy, compact, objects will have a higher terminal velocity than light, spread out objects. Therefore, heavy objects will fall faster in air than light objects

HW P144-145 Qs 1-6 Spectrum Phys.

3B 27/9/5

More ticker tapes. This time, we measured the motion of trolley rolling down a slope. You produced another ticker tape "graph" and calculated the acceleration of the trolley.

Remember: Acceleration = Change in speed / time

a = (v-u)/t

To work out acceleration you must first work out the fastest speed ( s = d/t ) from the longest ticker. Then work out the slowest speed ( s = d/t ) again from the shortest ticker. Then calculate how long the time was between the 2 speeds you have just worked out. Finally stick all 3 numbers into the formula for acceleration.

HW Finish graph and acceleration calculation if not already done. Complete the free fall ticker tape question sheet.

3B 23/9/5

We looked at calculating acceleration.

Acceleration is the rate of change of speed (as long as no change of direction is involved)

Acceleration (m/s²) = Change in speed / time

In symbols : a = (v-u)/t

v = final speed (m/s)

u = initial speed (m/s)

t = time to go between the 2 speeds

We did some example calculations. A timer ball was used to calculate the acceleration due to gravity (about 10m/s/s).

Books were taken in.

3H 22/9/5

More ticker tapes. This time, we measured the motion of trolley rolling down a slope. You produced another ticker tape "graph" and calculated the acceleration of the trolley.

Remember: Acceleration = Change in speed / time

a = (v-u)/t

To work out acceleration you must first work out the fastest speed ( s = d/t ) from the longest ticker. Then work out the slowest speed ( s = d/t ) again from the shortest ticker. Then calculate how long the time was between the 2 speeds you have just worked out. Finally stick all 3 numbers into the formula for acceleration.

HW Finish graph and acceleration calculation if not already done. Complete the free fall ticker tape question sheet.

3H 20/9/5

We looked at calculating acceleration.

Acceleration is the rate of change of speed (as long as no change of direction is involved)

Acceleration (m/s²) = Change in speed / time

In symbols : a = (v-u)/t

v = final speed (m/s)

u = initial speed (m/s)

t = time to go between the 2 speeds

Books were taken in.

3B 20/9/5

We looked at methods of measuring motion. Firstly, to work out the speed of an object you need to know how far it has travelled and how long it has taken.

We observed a light gate attached to an air track. The light gate times how long a beam of light is cut off for. If you know the length of the object, you can than calculate its speed.

Speed (m/s) = Distance (m) / Time (s)

Ticker tape timers were then introduced. They produce a dot on a strip of ticker tape once every 1/50th of a second (0.02s). The distance between the dots produced depends on how fast the ticker tape was moving through the machine at the time.

HW

• Complete your ticker tape graph.
• Put an explanation in your book including a diagram of how the ttt is used to measure speed.
• Use the fastest and slowest speeds from your graph as example speed calculations in your book.

We looked at drag forces.

Our example was ball bearings falling through a thick and viscous fluid. The large amount of drag allowed us to see the effect on the rate that they fell.

In air, (unless the object is very light), much higher speeds need to be reached.

The above shows how a parachutist first accelerates until the air resistance force on him is equal to his weight. He then travels at terminal velocity, a constant speed with balanced forces acting on him. He then artificially increases his air resistance by opening his parachute, so he slows down until air resistance once again equals his weight at a much slower (and safer) speed.

Terminal velocity occurs when the air resistance (sometimes called "drag") force equals the weight iof the falling object. This means that:

the object is falling with a constant velocity - its acceleration is zero.

heavy, compact, objects will have a higher terminal velocity than light, spread out objects. Therefore, heavy objects will fall faster in air than light objects

Books were taken in. William and any others who didn't, hand your book in to me on Monday!

3H 15/9/5

Ticker tape timers were then introduced. They produce a dot on a strip of ticker tape once every 1/50th of a second (0.02s). The distance between the dots produced depends on how fast the ticker tape was moving through the machine at the time.

HW Finish the tt homework sheet.

3H 13/9/5

We began to look at the motion of objects, and how you can measure them. Firstly, to work out the speed of an object you need to know how far it has travelled and how long it has taken.

We observed a light gate attached to an air track. The light gate times how long a beam of light is cut off for. If you know the length of the object, you can than calculate its speed.

Speed (m/s) = Distance (m) / Time (s)

Books were taken in.

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Two atoms bump into each other. One says 'I think I lost an electron!' The other asks, 'Are you sure?', to which the first replies, 'I'm positive'

3B 13/9/5

An object sitting on a table has 2 equal and opposite forces acting on it. Its own weight acts downwards and is counteracted by the reaction force that the table puts onto the object.

We did an experiment investigating friction. The larger the weight of an object, the larger the frictional force it can produce in contact with a surface. We discovered this because it took a larger force to start moving a block when it had masses piled on top.

Once an object has started sliding, the frictional force on it decreases. It took less force to keep the block sliding at a constant speed than it did to start it moving in the first place. Static friction is larger than dynamic friction.

HW 1. Finish the experimental write up including an evaluation.

2. Answer Qs 4-10 from Spectrum Physics P33 (we haven't mentioned this a lot so you will have to read the text book section!)

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There are 10 kinds of people in the world..... Those who understand Binary, and those who don't.

3B 9/9/5

Books were issued, and the first topic - forces was touched upon. Forces change the motion of an object. They can also change its shape.

Forces can be mechanical or act at a distance (e.g. gravity).

08/09/05 3H

Books were issued and we started the first topic of the year - forces.

Forces can be mechanical or act at a distance (e.g. gravity). When an object has unbalanced forces acting on it, it will accelerate in the direction of the overall force acting on it. If a body has balanced forces on it, it will remain at a constant speed, or at rest.

An object sitting on a table has 2 equal and opposite forces acting on it. Its own weight acts downwards and is counteracted by the reaction force that the table puts onto the object.

We did an experiment investigating friction. The larger the weight of an object, the larger the frictional force it can produce in contact with a surface. We discovered this because it took a larger force to start moving a block when it had masses piled on top.

Once an object has started sliding, the frictional force on it decreases. It took less force to keep the block sliding at a constant speed than it did to start it moving in the first place. Static friction is larger than dynamic friction.

HW Finish the write up of the experiment by ensuring that the graph is finished and Qs 7-10 from the handout are answered in your book.

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Q: How does the barber cut the Sun's hair? A: Eclipse it.