Motion, Speed, and Velocity

THE NEED FOR SPEED!!!THE NEED FOR SPEED!!!

http://www.youtube.com/watch?v=dKDDrnx-Fgw

Motion

• When an object changes its position, motion has occurred.– Distance- How far an object has moved.– Displacement- How far an object has moved in

relation to its starting point.– Consider direction

Example: Two runners travel along the same straight path in a straight line for 500 meters. At the end of the run their distances are the same but their displacements are different. How can this be so?

Speed- Distance an object travels per unit of time

Relationships between speed, distance, and time:

Speed = Distance/ Time = d/ t » Constant Speed- speed does not change

over time» Average Speed- speed of motion when

speed is changing

Avg Speed = Total Distance/ Total Time

» Instantaneous Speed- speed at any given moment in time (speedometer)

Graphing Motion

• Graph distance on the y-axis and time on the x-axis

Slope = Slope = riserise = = distancedistance = speed = speed

run timerun time

Distance - Time Graph

• If something is not moving, a horizontal line is drawn.

• If something starts out slow and then speeds up, its change in speed can look like this.

Learning Checkpoint

This graph shows several stages of motion:

•Stage 1: 100 m in 10 s

•Stage 2: 50 m in 10 s

•Stage 3: 150 m in 20 s

Calculate the speed as indicated by each of the colors.

Calculate the average speed.

What is the total distance?

What is the displacement?

Solution

Stage 1: S= d/ t

100 m/ 10 s= 10 m/s

Stage 2: S= d/t

50 m/ 10 s= 5 m/s

Stage 3: S= d/t

150 m/ 20 s= 7.5 m/s

Ave Speed= Tot d/ Tot t

300 m/ 40 s= 7.5 m/s

Distance = 300 meters

Displacement = 0 meters

3.1 Calculating speed

3.1 Calculating speed• The change in position

is a distance traveled in a given amount of time.

• To calculate the speed of an object, you need to know two things:– the distance traveled

by the object– the time it took to

travel the distance

Interpreting a distance versustime graph

1. How many stops does it make?

2. What is the boat’s average speed for the whole trip?

3. What is the highest speed the boat reaches?

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.

1. The boat makes three stops because there are three horizontal sections on the graph.

2. The average speed is 10 km/h (100 km ÷ 10 h).

3. 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.

Velocity

• The speed and direction of an object’s motion.

– This car is moving 88 km / hr south

Velocity MUST include a

reference direction!

3.3 Working with Equations

If a car moves with an average speed of 60 km/hr for an hour, it will travel a distance of 60 km. How far will it travel if it continues this average rate for 4 hrs?

A runner makes one lap around a 200 m track in a time of 25.0s. What was the runner's average speed?

A motorist travels 406 km during a 7.0 hr period. What was the average speed in km/hr and m/s?

A bullet is shot from a rifle with a speed of 720 m/s. What time is required for the bullet to strike a target 3240 m away?

What is the average speed of a cheetah that sprints 100 m in 4 s? How about if it sprints 50 m in 2 s?

REVIEW

• F=MxA • Force=Mass X Acceleration

Review

• A man hits a golf ball (0.2 kg) which accelerates at a rate of 20 m/s2. What amount of force acted on the ball?

Review

• You give a shopping cart a shove down the isle. A cart is full of groceries and has a mass of 18 kg. The cart accelerates at a rate of 3 m/s2. How much force did you exert on the cart?

Review

• What is the acceleration of a 18 kg mass pushed by a 9 N force?

Review

• Given a force of 88 N and a acceleration of 4 m/s2, what is the mass?