Chapter 11 Motion

Position Position- a place or location –Positions may be described differently by the groups, but the distance/displacement is the same Frame of Reference- A frame of reference is any object (s) that are considered to be stationary from which motion can be measured. (the point of view) –Any frame of reference can be chosen (no one is correct), but a frame of reference must be chosen to have any meaning

Distance and Displacement Distance: “how much ground an object has covered” during its motion. –Depends on path taken –Not negative, not zero Displacement: “how far out of place an object is” (the change in position) –Only measuring length from start to finish –Does not depend on path taken –Has a direction (can be negative, can be zero)

Distance = 4 m + 2 m + 4 m + 2 m = 12 m Displacement = 0 m –You are exactly where you started.

Speed vs. Velocity Speed: How fast an object is moving –Average Speed = distance traveled/ time Ex: 35 mi/hr Velocity: The rate at which an object changes its position –Average Velocity = displacement/time –Speed with a direction Ex: 35 mi/hr North

Instantaneous Speed – the speed at any given moment of time –found by calculating the slope of a distance-time graph at one point. –The speedometer tells you the instantaneous speed. Average speed and instantaneous speed can be equal but they are not always equal.

Graphing motion – distance-time graphs Distance-time graph A distance-time graph tells us how far an object has moved with time. The steeper the graph, the faster the motion. A horizontal line means the object is not changing its position - it is stationary. A downward sloping line means the object is returning to the start.

Acceleration Acceleration – the change in velocity over time. –If you change speed or change direction you are accelerating. Acceleration = speed 2 – speed 1 t ime 2 – time 1 t ime 2 – time 1 –Units: m/s 2, meters/second squared or meters per second per second. (km/hr/sec) –Meaning: every second you are increasing/decreasing your speed by so many meters/second.

Deceleration – negative acceleration (slowing down). –The motion of the object is opposite to the direction of the acceleration.

Velocity time graphs A speed - time graph shows us how the speed of a moving object changes with time. – –The steeper the graph, the greater the acceleration. – –A horizontal line means the object is moving at a constant speed. – –A downward sloping line means the object is slowing down.