Speed vs. Velocity Lesson

Speed vs. Velocity Lesson

S8P3. Obtain, evaluate, and communicate information about the cause and effect relationships between force, mass, and the motion of objects.

a. Analyze and interpret data the identify patterns in the relationship between speed and distance, and velocity and acceleration.

In the previous lesson, you learned that motion can be described in terms of postion, direction, and speed. Is there another way we can describe the motion of objects?

Is there another way we can describe the motion of objects?

Imagine that two birds leave the same tree at the same time. They both fly at 10 km/h for 5 minutes.

Why don't they end up at the same place?

The birds went in different directions. Their speeds were the same, but they had different velocities.

Describing Motion

Imagine you were visiting Clissold Park. A friend stopped by the park to spend the day with you. If you were at the Lodge House and your friend was coming in the Robinson Crusoe Gate, how would you give him/her directions? How would you know what time he/she might reach you?

Answer: You would use both direction and speed.

Velocity

• Velocity is the speed of an object in a particular direction.

The speed of the cars may be similar, but the velocity of the velocity of the cars differ because the cars are going in different directions.

Speed Vs. Velocity

• Speed and velocity both measure how fast an object is going.

• Speed and velocity are both measured in the same unit meters/second (m/s).

• Velocity includes the direction of the motion, but speed does not include direction.

Read the statements on the following slides and determine whether they are examples of speed or velocity.

Multiple Select

Example #1: The plane is traveling 600 km/h.

• speed

• velocity

Multiple Select

Example #2: The bus is traveling 20 m/s south

• speed

• velocity

Multiple Select

Example #3: The bicycle is moving 3 m/s north

• speed

• velocity

Multiple Select

Example 4: The jogger is running 1 m/s.

• speed

• velocity

Open Ended

Suppose a car is traveling at a speed of 40 km/h north and then turns left at an intersection and continues on with a speed of 40 km/h. At what point did the velocity change?

Answer: The speed of the car is constant at 40 km/h, but the velocity changes from 40 km/h north to 40 km/h west when the car turns.

Directions: Read the scenario below. Identify the point(s) when velocity changes.

A bus traveling at 15 m/s south speeds up to 20 m/s south. The bus continues to travel at the same speed but changes direction to travel east. The bus slows down and swerves north to avoid a cat.

Answer

A bus traveling at 15 m/s south speeds up to 20 m/s south. The bus continues to travel at the same speed but changes direction to travel east. The bus slows down and swerves north to avoid a cat.

Distance- Time Graphs

Describing the motion of an object is occasionally hard to do with words. Sometimes graphs help make motion easier to picture, and therefore understand.

Plotting Distance Against Time

• Time is always plotted on the x-axis (bottom of the graph). The further to the right on the axis, the longer the time from the start.

• Distance is plotted on the y-axis(side of the graph). The higher up the graph the further from the start.

Open Ended

Match the descriptions to the correct graphs in the picture to the left. (You can click on the picture to enlarge it.)

Answer

Matching

Match the part of the graph to the description:

1. Stationary

2. Increasing speed

3. Slow and constant speed

4. Fast and constant speed

5. Returning to start

Summary

- The steeper the graph, the faster the motion.

- A horizontal line means the object is not moving. It is stationary.

- A curve line means the speed is changing by speeding up or slowing down.

Open Ended

Practice Problem #1: Who ran at a constant velocity for 30 minutes?

Open Ended

Practice Problem #2: Who stopped running for 5 minutes?

Open Ended

Practice Problem #3: If Runner B continued to run at the same average speed, how far would she have run after 1 hour?

Answers for Practice Problems 1-3

• Practice Problem #1: Runner B

• Practice Problem #2: Runner C

• Practice Problem #3: 12 km/hr