Chapter 1

Motion & Momentum (without the momentum)

Motion

•      All matter is constantly in motion

–   Atoms constantly move

•      Motion involves change in position

•      An object changes position relative to a reference point

•      Distance is the total length of the route an object travels when it moves

•      Displacement includes distance                             and direction of the stopping point                               from the starting point

Speed

•      Speed is distance traveled divided by the time it takes to travel the distance

–   Speed = Distance/Time

–   Ex:  You travel 100 meters in 5 seconds

–   Ex:  You travel 525 meters in 25 seconds

•      The units of speed are ‘distance per time’

–   Meters per second (official SI unit)

–   Miles per hour

Speed

•      An object in motion can change speeds many times as it moves from one point to another, speeding up or slowing down

•      Average speed is the total distance traveled divided by the total time taken

•      An object’s speed at a particular moment in time is called instantaneous speed

•      Constant speed occurs when an object travels at a steady rate

Graphing Motion

•      Motion can be graphed on a distance-time graph with time plotted on the horizontal axis and distance plotted on the vertical axis

Graphing Motion

•      The steeper the line on a distance-time graph, the greater the speed

•      A horizontal line on a distance-time graph indicates that no change in position is occurring, and the speed is zero.

Velocity

•      Velocity is the speed of an object and its direction of motion

–  Velocity changes if either, or both, of these changes

•      Ex:  10 m/s  vs. 10 m/s north

Acceleration

•      Acceleration is a change in velocity divided by the time for the change to occur

–   It can include when an object:

•    Speeds up

•    Slows down

•    Changes direction

•      You walk 0.5 m/s north and then turn left at the same speed.  Did you accelerate?

•      You walk 0.5 m/s north and then slow to 0.25 m/s north.  Did you accelerate?

Acceleration

Calculating Acceleration

•      Acceleration can be calculated if you know how an object’s velocity has changed during a given time period

•      The formula for calculating acceleration:

–  Acceleration = (Final Speed-Initial Speed) / Time

–  A = (s_f – s_i) / t

•      Ex:  You start at 0 m/s and begin running. You top out at 5 m/s.  This took you 10 s. What was your acceleration?

Calculating Acceleration

•      The unit for acceleration is distance divided by time squared.

–  In SI units, meters per second squared (m/s²)

•      Acceleration is positive when an object speeds up and negative when an object slows down

Graphing Acceleration

•      Accelerated motion can be graphed, with speed on the vertical axis and time on the horizontal axis

Graphing Acceleration

•      An object that is speeding up will have a line on a speed-time graph that slopes upward

•      An object that is slowing down will have a line on a speed-time graph that slopes downward

•      A horizontal line                                  would indicate                             acceleration of zero,                                 or constant speed.