Unit 3: Motion, Forces, & Energy

Chapter 9: Motion & Energy

Big Idea: You can describe the motion of an object by its position,

speed, direction, & acceleration

Mrs. Lee - Ch 9 2

4 Sections

1. Describing Motion

2. Speed & Velocity

3. Acceleration

4. Energy

Mrs. Lee - Ch 9 3

Sec 1: Describing Motion

KEY CONCEPTS

• An object is in motion if it changes position relative to a reference point

• Distance is the total length of the actual path between 2 points. Displacement is the length & direction of a straight line between starting & ending points

Mrs. Lee - Ch 9 4

Sec 1: Key Terms

• Motion• Reference point• Distance• Displacement• Vector

Mrs. Lee - Ch 9 5

Sec 2: Speed & Velocity

KEY CONCEPTS• To calculate the speed of the object, divide

the distance the object travels by the time it takes to travel that distance

• Speed = Distance Time

• Changes in velocity may be due to changes in speed, changes in direction, or both

Mrs. Lee - Ch 9 6

Sec 2: Speed & Velocity (cont’d)

• The slope of a distance vs. time graph represents speed -- the rate that distance changes in relation to time

• Slope = Rise

Run

Mrs. Lee - Ch 9 7

Sec 2: Key Terms

• Speed• Average speed• Instantaneous speed• Velocity• Slope

Mrs. Lee - Ch 9 8

Sec 3: Acceleration

KEY CONCEPTS• In science, acceleration refers to:

1) increasing speed2) decreasing speed

or 3) changing direction• To determine the acceleration of an object,

you must calculate its change in velocity per unit of time

Mrs. Lee - Ch 9 9

Sec 3: Acceleration (cont’d)

• Acceleration = Final velocity – Initial Velocity

Time• You can use both a speed vs. time graph & a

distance vs. time graph to analyze the motion of an accelerating object

Mrs. Lee - Ch 9 10

Sec 3: Key Terms

• Acceleration

Mrs. Lee - Ch 9 11

Sec 4: Energy

KEY CONCEPTS• The kinetic energy of an object depends on

both its mass & its speed• Kinetic Energy = 1 x Mass x Speed2

2• An object’s gravitational potential energy

depends on its weight & on its height relative to a reference point

Mrs. Lee - Ch 9 12

Sec 4: Energy (cont’d)

• Gravitational potential energy =

Weight x Height

• Mechanical energy =

Potential energy + Kinetic energy

Mrs. Lee - Ch 9 13

Sec 4: Energy (cont’d)

• Any object that rises or falls experiences a change in its kinetic & gravitational potential energy

• According to the law of conservation of energy, energy cannot be created or destroyed

Mrs. Lee - Ch 9 14

Sec 4: Key Terms

• Work• Energy• Kinetic energy• Potential energy• Gravitational potential

energy

• Elastic potential energy

• Mechanical energy• Law of conservation

of energy