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
4 Sections
1.
2.
3.
4.
Describing Motion
Speed & Velocity
Acceleration
Energy
Mrs. Lee - Ch 9
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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
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Sec 1: Key Terms
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Motion
Reference point
Distance
Displacement
Vector
Mrs. Lee - Ch 9
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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
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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
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Sec 2: Key Terms
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Speed
Average speed
Instantaneous speed
Velocity
Slope
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Sec 3: Acceleration
KEY CONCEPTS
• In science, acceleration refers to:
1) increasing speed
2) 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
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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
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Sec 3: Key Terms
• Acceleration
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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
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Sec 4: Energy (cont’d)
• Gravitational potential energy =
Weight x Height
• Mechanical energy =
Potential energy + Kinetic energy
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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
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Sec 4: Key Terms
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Work
• Elastic potential
energy
Energy
• Mechanical energy
Kinetic energy
• Law of conservation
Potential energy
of energy
Gravitational potential
energy
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