5C+5B 14/03/05
Triplers did some momentum past paper questions. We'll go through these and then practise some circular motion questions on Thursday.
All will be furnished with papers to take away for Easter on Thursday.
5C+5B 11/03/05
When a force acts on a body, it causes a change in momentum. The larger the dorce, the larger the change in momentum. The longer the force acts on the body, the larger the change in momentum it causes.
Force * time = Change in momentum
Ft = mv - mu
This is a rearrangement of Newton's 2nd law which can help explain why certain safety measures are used. Crumple zones are used in cars to increase the time it takes for the car to slow down and stop as it crashes. A smaller force acts on the car for a longer time - this reduces the chance of occupants injuring themselves.
Momentum is finished as a topic now, we'll have a test during Monday's lesson.
Circular motion was started. This rests on the idea that an object moving in a circle is always changing direction, even if it is travelling at a constant speed.
Velocity is a speed plus direction (it is a vector) and so an object moving in a circle has a constantly changing velocity (due to direction changing). Any object with a changing velocity has an acceleration. In this case, the acceleration is towards the centre of the circle.
An acceleration is always caused by a force acting. In this case the force must be acting towards the centre of the circle. An object in a cirular orbit uses gravity, a ball whirled round on a piece of string uses tension in the string, but all objects moving in a circle have a force acting towards the centre of the circle called the centripetal force.
5C+5B 07/03/05
Momentum is always conserved in collisions.
The force between 2 vehicles is equal and opposite during the crash. They experience equal and opposite changes in momentum during the crash (so total momentum must stay the same). The same change in momentum requires less change in velocity for a heavier object.
Occupants of a heavier truck experience less force during a head on crash. This is because the big truck experiences less deceleration, (or negative acceleration). The force on the people in the truck is: F = ma , where m is the mass of the person. People inside the truck must decelerate at the same rate as the truck (unless they go flying out through the windscreen). A large force is what will hurt people in a crash.
Kinetic energy is rarely conserved in collisions. If it is, the collision is elastic.
If you are told that a collision is elastic, you have more information to solve problems mathematically.
Doublers started work on self assesment quizzes. These can help give you a good idea of what areas you need more work on.
HW Complete the sheet of momentum questions. We'll have a test on momentum next Monday.
5C+5B 03/03/05
We went through the Earth in Space test. Doublers continued their past paper.
Triplers were shown some demonstration collisions. Apart from some small errors due to friction, the total momentum of bodies before a collision was always the same as the total momentum after a collision.
Momentum = Mass * velocity
In a car accident the larger mass vehicle is less likely to change velocity by so much. Both vehicles involved in the crash will experience equal and opposite forces when they collide, and so equal and opposite changes in momentum. However, a lighter vehicle has to change its velocity more to exhibit the same change in momentum as a heavier vehicle. That means the people inside the smaller veicle experince a greater deceleration and so a greater force during the crash and are more likely to die.
This graph shows the trend of fewer deaths in heavier vehicles.
An elastic collision is a special case where the total kinetic energy of all the bodies stays the same before and after the collision.
KE = 1/2mv2
Kinetic energy does not have direction, so all KEs are positive. (It is a scalar not a vector quantity.)
HW P93 AQA Qs 4-8 (triplers) Coursework sorting (doublers)
5C +5B 28/02/05
We sat the Earth in Space test. A brief instruction in how to solve all problems when 2 objects collide was given.
1. Draw both objects and mark in their mass and velocity.
2. Calculate the combined total momentum (add them together remembering that only one direction is positive.)
3. Draw a new diagram showing what has happened after the collision.
4. The total momentum afterwards must equal the total momentum before the colliosion. Use this fact to work out any unknowns.
5C +5B 25/02/05
We looked at possible fates of the universe. Redshidt gives us evidence that it is expanding now. We infer from this that it started off much smaller (e.g. the Big Bang.) The future of the universe is dependent on how much matter there is to gravitationally cause it to recollapse.
Case A is a universe without enough matter to slow the expansion much. Case C is where there is enough mass to cause a "Big Crunch". Case B is the dividing case between the 2. This is a universe with critical density of matter.
In actual fact recent evidence suggests that the expansion of the universe may be accelerating so there may be other forces at work as yet not understood.
HW Test on Earth and beyond next time.
5C +5B 21/02/05
We looked at methods of finding out how far away objects in the rest of the galaxy and universe are. One example is parallax.
Cosmic distances can be measured in au (distance from the Earth to the Sun) or in light years (distance travelled by a beam of light in 1 year). The nearest star is 4 light years away. Our galaxy is 100000 light years in diameter. Galaxies are separated by millions of light years.
When an object is moving compared to an observer, any waves that it produces are shifted in wavelength slightly. If an object is moving away from you, the waves get longer. The Doppler effect occurs in sound when cars drive past you at speed.
This happens in the light from distant stars and so the light appears redder or bluer than it should do. Edwin Hubble looked at the light in a number of distant objects in the sky. He realised that they were very nearly all moving away from the Earth - the light had been redshifted. The further away the objects were, the more their light was redshifted - the faster they were moving away.
If you were to reverse the direction of everything in the universe (i.e. reverse time), then everything would be travelling back towards a single point in time and space. This is where the Big Bang theory started.
5C +5B 10/02/05
The nine planets are not the only objects in the solar system. Between Mars and Jupiter there is a belt of small rocky objects called the asteroid belt. Outside Neptune there are many icy objects, of which Pluto may just be a large example rather than a true planet. This is called the Kuiper belt. Sometimes these are disturbed and travel towards the Sun as comets. The tail is due to the Sun's heat evaporating off material from the comet's nucleus.
Handout covering orbits and the solar system is available here
Then we looked at stars. They are fuelled by nuclear fusion reactions at their centres which release enormous amounts of energy. Mainly, hydrogen is fused into helium. They are prevented from exploding by the very strong force of gravity keeping them together.
Stars eventually run out of hydrogen at their core and so gravity pulls their cores into an even denser, hotter state. The outside of the star expands massively and it becomes a red giant. Helium can then start to fuse into heavier elements. However, eventually the star will run out of fuel and meet its end. Depending on how big the star is it can leave one of 3 different types of remnant.
Small ones become white dwarves (like the Sun)
Larger ones blow up at the end of their life in a supernova and become neutron stars (like a huge nucleus, full of just neutrons)
Even bigger than that and they become black holes.
HW Answer Qs 8-11 on P152 of AQA book.
5C +5B 7/02/05
RM absent. You did Earth in Space questions from P143-144 of the AQA book.
5C +5B 3/02/05
The Earth rotates once every 24 hours. It orbits the Sun once every 365.25 days. Circular orbits are possible due to the force of gravity. If the combination of the motion of a body sideways, and the vertical acceleration it has due to gravity make up a curved path which follows the curvature of the Earth, it is in orbit. It must be above the atmosphere so the only force acting on it is gravity towards the centre of the Earth.
The larger the orbit, the slower a satellite must travel, due to a diminishing gravitational force from the Earth. There are several different types of orbits used by artificial satellites.
Low Earth Orbit is just high enough to avoid atmospheric drag. They can orbit once in as little as 90 minutes. Polar orbits allow satellites a close up view of the whole Earth (as it spins beneath them). This is useful for weather and spy satellites.
A geostationary orbit is much higher, completing one orbit in exactly one day. This is very useful for communications satellites as they are always above the same point on the Earth.
Site containing lots of information about satellites
HW An essay "I do/do not believe that there is life elsewhere in the universe" Use the information sheet provided and other research to help you. Mention what qualities a planet must have for life as we know it.
5C 31/01/05
We finished going through the mock. Onto new things on Thursday. Syllabi for the Earth and beyond topic were issued.
Coursework submissions for all by Thursday or det. LD, AA, and JD are seeing me Tues lunch at 12.50 about theirs.
5B 31/01/05
We finished going through the mock. Onto new things on Thursday.
Coursework was returned to those who definately have some work to do. Others haven't yet submitted final versions. Remember, if I don't have a hard copy, you don't get any marks.
5B 27/01/05
We went through questions 1-10 of the mock. I informed those whose coursework submissions were not up to scratch.
5C 27/01/05
We went through questions 1-10 of the mock. Complete coursework submissions are required from everyone by next week. Only those which require further alteration will then be given back.