Chapter 4 - Motion

Frames of Reference

• Is this train in motion?• How do you know?

Frames of Reference

• Frames of reference help us to describe the motion of something

Frames of Reference

• RELATIVE MOTION is movement in relation to a frame of reference.

Frames of Reference

Frame of Reference

Object Relative Motion

You – on a moving bus

Your friend – in a nearby seat

You – on a moving bus

Your friend – standing at the bus stop

You – standing at the bus stop

Your friend – on the moving bus

Measuring Distance

• Distance is the length between 2 points• When measuring the length, be sure to

include units (cm, km, m)

Measuring Displacement

• Displacement is direction + length between starting and ending points

Displacement Along a Straight Line

• A VECTOR is a quantity the describes size, length or amount, and direction– Same direction = add them– Opposite directions = subtract the difference

– Example: Figure 4.2 on page 78

Displacement That Isn’t Along a Straight Path

• Use graphing to help determine displacement• Displacement is always shorter than or equal

to the distance

QUICK LAB!!!

• Using graph paper and rulers, draw a path on your paper with at least 3 turns. Measure the total distance of the path and displacement.

Review!

• What’s a frame of reference?• What’s is distance?• How is displacement different than distance?

4.1 Vocabulary

• Speed• Average speed• Instantaneous speed• velocity

Speed

• SPEED is the ratio between the distance an object travels to the amount of time is takes

• Example: 50 miles/hour

Average Speed vs. Instantaneous Speed

• Average speed = total distance/total time– Formula: s = d/t

• Instantaneous Speed = how fast something is moving at any given movement– Example: a speedometer in a car measures

instantaneous speed

Graphing Motion

• The slope of a line on a distance-time graph is speed

• The steeper the slope, the faster the speed!• Check out page 83-84 for comparing graphs!

Velocity

• Speed in a given direction!• Velocities in the same direction are added• Velocities in opposite directions are

subtracted

4.3 Vocabulary

• Acceleration• Free fall• Constant acceleration• Linear graph• Nonlinear graph

What is acceleration??

• Acceleration = rate at which velocity changes• Can be described as a change in speed,

change in direction, or change in both• The rate of acceleration, due to gravity is

9.8m/s/s

Changes in Speed

• FREE FALL – movement of an object toward Earth solely because of gravity

Changes In Direction• You can accelerate even if your speed is

constant!• Example: the speed may be constant on a

carousel, but the direction is always changing

Changes in Speed and Direction

• Sometimes speed and direction can change at the same time

• Example: riding a roller coaster!

Constant Acceleration• A steady change in velocity• The velocity of the object changes by the

same amount each second

Calculating Acceleration

• Acceleration = change in velocity/total time– Formula = (vf – vi)

t

• Complete the Math Practice problems on page 346

Graphs of Accelerated Motion

• The slope of a speed-time graph is acceleration

• Check out pages 86 & 89 for graphing examples!