1 Measuring Motion

Measuring Motion

How do you know something is moving?

An object in outer space appears to be stationary in space. How can we tell it is moving or not moving???

Do these answers work for determining is something is moving on Earth?

Point of reference

An object that stays in place compared to an object that is moving.

Examples: North Star, mountains on Earth, buildings, trees, etc

Motion

An objects change in position relative to a reference point.

Time = x-axis

Distance = y-axis

.

This line is not horizontal (at rest)

Speed Vs. Velocity

Speed = Rate at which distance changes over time. S = D/t

Velocity = speed with direction V = D/t with a direction (right, left, north, south, negative, positive)

ExampleA bus moves a distance of 150 m East in 10 seconds.

A. What is the bus’s average speed?

B. What is the bus’s average velocity?

C. What are the passengers on the bus’s average velocity (assume no passengers are moving)?

D. If a passenger stands up and starts moving 1 m/s East, what is the passengers total velocity?

E. If another passenger stands up and starts moving 1 m/s West what is the passengers total velocity?

A. S = 150 m/10 s Speed = 15 m/s

B. V = 150 m/10 s Velocity = 15 m/s East

C. Passengers on the bus move at the same rate as the bus as long as it is not moving. (15 m/s East)

D. 15m/s East + 1 m/s East = 16 m/s East

E. 15 m/s East – 1 m/s West = 14 m/s East

Acceleration

The rate at which velocity changes over time

Avg Acceleration = Final Velocity – Starting Velocity

time it takes to change velocity

What is the bicyclist’s acceleration?

Velocity Versus Time Graph

1. What is happening from 0 seconds to 8 seconds?

2. What is happening from 8 to 10 seconds?

3. What happens at exactly 8 seconds?

4. What happens to this person’s position from 0 –10 seconds?

Circular Motion• Objects moving in circle always change

direction, velocity, and acceleration

Black arrow indicates direction of motion and velocity. Blue arrow indicates acceleration.