Uniform Motion

Uniform Motion Uniform = “Constant” Neither the speed nor direction can change. Direction: must be moving in a straight line, forward or back OR up or down. Speed: can not be speeding up or slowing down.

Speed A term used to describe motion. Average speed is the distance an object moves in a certain length of time. Speed = ∆ distance ÷ ∆ time Speed is a scalar quantity so it has only magnitude (a number and units) and does not include direction. Instantaneous speed is the speed at a specific instant in time.

Q: When would you use average speed? A: When discussing the pace you were travelling during a trip. Ex. It took me one hour to drive to Truro 100 km away, so my average speed was 100 km/h. Q: What instrument in your car measures instantaneous speed? A: Speedometer. Q: When does instantaneous speed matter? A: When you are passing a police officer using a speed gun, which measures your speed at a specific instant.

Velocity Velocity describes an object’s displacement during a specific time interval. Velocity is a vector quantity. Velocity has both magnitude and direction. Ex. 56 km/h West OR -9.8 m/s

Constant and Average Velocity When an object travels at the same speed and the same direction for a time interval, it has constant velocity. Average velocity: the displacement of an object divided by the time interval it takes to travel the displacement.

Speed Graph Also called Distance-Time Graph Distance is on the “y” axis. Time is on the “x” axis. The slope of the line (how steep it is) is the speed.

Graph shapes of uniform motion

Uniform or Non-Uniform?

Uniform

The position-time graph that represents "uniform motion" is:

Slope or “Speed” Rise ÷ Run “Rise” (y-axis) is your change in distance (how far you went) “Run” (x-axis) is your change in time (how long it took)

Step 1: Pick two points on the graph Step 2: Write down the coordinates and label (x1, y1) (x2, y2) Step 3: Calculate the rise (y2 – y1) Step 4: Calculate the run (x2 – x1) Step 5: Divide the rise (∆y) by the run (∆x) (x2, y2) (11:30, 200km) * * (x1, y1) (9:30, 40km) Rise = (y2 – y1) Rise = (200 – 40) Rise = 160 km Run = (x2 –x1) Run = (11:30-9:30) Run = 2 hours Speed = Rise / Run Speed = 160 km / 2 hr Speed = 80 km/hr

Calculate the speed. Speed = d/t or rise/run (200, 5000) Calculate the speed. Speed = d/t or rise/run Speed = (5000 – 1000) ÷ (200 – 40) Speed = 4000 m ÷ 160 s Speed = 25m/s (40, 1000)

1st: Constant speed to the right. ∆d = 60m – 0 m; ∆d = 60m ∆t = 10s – 0s; ∆t = 10s Speed = ∆d / ∆t; Speed = 60m/10s; Speed = 6m/s 2nd: Stationary (not moving). 3rd: Constant speed to the left (straight line) ∆d = -40m – 60m; ∆d = 100m ∆t = 40s – 15s; ∆t = 25s Speed = ∆d / ∆t; Speed = 100m/25s; Speed = 4m/s 4th: Constant speed to the right (straight line) ∆d = 0m - -40m; ∆d = 40m ∆t = 60s – 40s; ∆t = 40s Speed = ∆d / ∆t; Speed = 40m/20s; Speed = 2ms