Motion Graphs SCI 10 Physics

Remember: Position-Time Graphs show an object’s change in position as time passes. These graphs include direction. Distance-Time Graphs show an object’s total distance travelled as time passes. These graphs can only be increasing.

Example: Susan walks to the store which is 10 km away. She then walks back home.

Uniform Motion Motion in which the object’s displacement is equal for each time interval. Example: For every 2s, the displacement is 3m [E]. So you would see a table like this: Time (s) Position (m) 2 +3 4 +6 6 +9

Uniform Motion When the object’s displacement is not consistent, then the motion is not uniform.

Uniform Motion Non-Uniform Motion

Uniform Motion A position-time graph will show uniform motion as a straight line, connecting all data points.

Uniform Motion If our data is not perfectly uniform, we can show it as uniform by drawing a line of best fit.

Are these people moving fast or slow? How can we tell? Person A – Slow – The line is not very steep Person B – Fast - The line is very steep B A

Slope - The steepness of a line. The slope of a distance-time graph will tell us how fast the object is moving. The speed of the object. The slope of a position-time graph will tell us hoe fast the object is moving and in what direction. The velocity of the object.

Describing Motion Graphs

Describing Motion Graphs

Describing Motion Graphs

Describing Motion Graphs Positive Slope Towards the reference point

Describing Motion Graphs Positive Slope Away from the reference point

Describing Motion Graphs Negative Slope Towards the reference point

Describing Motion Graphs Negative Slope Away from the reference point

Describing Motion Graphs Zero Slope Object is not moving (no change in position) We say “at rest”

Interpreting a distance versus time graph This distance versus time graph shows a boat traveling through a long canal. The boat has to stop at locks for changes in water level. How many stops does it make? What is the boat’s average speed for the whole trip? What is the highest speed the boat reaches?

The boat makes three stops because there are three horizontal sections on the graph. The average speed is 10 km/h (100 km ÷ 10 h). The highest speed is 20 km/h. The position changes by 20 km in one hour for the first, third, and fifth hours of the trip.

Calculating Slope The slope of the line indicates speed. A steep line (red): Less time to cover a distance Higher speed A less steep line (green): More time to cover a distance Slower speed

Calculating Slope Rise over Run

Example A meerkat

Example A meerkat moves to the right of its den.

Example Another meerkat is initially 1.5m to the right of its den and moves to the left of it.

Example A third meerkat is standing upright 2m to the right of its den.

Practice Describe Ray’s drive to work at each interval. Include distance, time, speed, and direction.

For each situation below, sketch a position-time graph.   Sarah walks to the mall at a constant pace. She realizes she left her wallet at home so she gets a drive back to get it. Dylan runs halfway to his friend’s house at a constant pace. He gets tired and walks the rest of the way, still at a constant pace. Jill is driving to her friend’s house at a constant pace. She approaches a stop sign and makes a full stop. Then she starts driving again, reaching a constant pace to continue to her friend’s house.