Unit 3.1 Notes

What is Energy?

Energy – the ability to do work or cause change

What is the major source of energy for a human

body?

Energy is measured in the units of joules (J).

On food’s nutritional facts, you see calories. A

calorie is a unit of energy but not a metric unit.

1 food calorie = 4.2 kilojoules or 4200 joules

Work and Energy

Work – the transfer of energy

Work is measured in the units of joules (J) just like

energy.

An object must have energy in order to “do work.”

Example: Johnnie must have enough energy to lift a 20 kg

box

Energy has to be transferred from Johnnie to the

box in order to “do work”

Power and Energy

Power – the rate at which energy is transferred

Power = Amount of Energy Transferred (J)

Time (sec)

= J = Watt (W) is the unit for power

s

Which has more power to lift a leaf 5 m off the ground, a tornado or a breeze?

The tornado and the breeze do the same amount of work since they both need the energy to lift the leaf.

The tornado can apply the energy more quickly than the breeze, so it has more power.

Kinetic Energy

Kinetic Energy (KE) – energy an object has due to its motion

The word kinetic comes from the Greek work kinetos which means moving.

Examples of kinetic energy: a swinging hammer, a ball being thrown, or the basketball going in the net at the buzzer after UK loses to Louisville in basketball this year just like football!!

Kinetic Energy

The KE of an object depends on its mass and

its velocity (velocity is speed and a direction).

For example: You have a bowling ball and a golf

ball; they have different masses. If they are

released with the same velocity, the bowling

ball will have more KE since it has more mass

Kinetic Energy

Kinetic Energy = (½) x (mass) x (velocity)2

= (½) x (mass) x (velocity) x (velocity)

MATH NOTE: Remember 22 = 2 x 2 = 4

The bowling ball and golf ball example from the

previous slide will explain further:

Bowling Ball Golf Ball

Mass

(different) 7 kg (16 lbs.) 0.46 kg (0.101 lbs.)

Velocity

(same) 15 meters/sec (35 mph) 15 meters/sec (35 mph)

Kinetic Energy KE = (.5) x (mass) x (velocity) 2

= (.5) x (7 kg) x (15 m/s) x (15 m/s)

= 787.5 J

KE = (.5) x (mass) x (velocity) 2

= (.5) x (0.46 kg) x (15 m/s) x (15 m/s)

= 51.8 J

Potential Energy

Potential Energy (PE) – stored energy

that results from the position or shape of

an object.

There are two forms of potential energy:

Gravitational Potential Energy and

Elastic Potential Energy

Gravitational Potential Energy

Gravitational Potential Energy – potential energy

of an object that is directly related to how high the

object is off the ground.

Gravitational PE depends on weight and height.

Gravity pulls all objects toward the Earth’s

surface.

The greater the height of an object, the greater

the potential for gravity to pull the object.

Gravitational Potential Energy

Example: Two skiers that weigh the same are at

two different heights. The skier at the greater

height will have more potential energy due to

gravity.

Same Weight, Different Height Different Weight, Same Height

Gravitational Potential Energy

Gravitational PE = (weight) x (height)

Same Weight, Different Height

Red Skier Blue Skier

Weight

(same) 500 N 500 N

Height

(different) 12 meters (40 ft) 18 meters (60 ft)

Potential

Energy GPE = (weight) x (height)

= (500 N) x (12 m)

= 6000 J

GPE = (weight) x (height)

= (500 N) x (18 m)

= 9000 J

NOTE: Weight in science is measured in

NEWTONS (N).

Weight and mass are not the same thing.

Weight = (mass) x (the force of gravity)

Elastic Potential Energy

Elastic Potential Energy – the potential

energy associated with objects that can

be compressed or stretched.

Examples: spring, slingshot, bow

exists as measured in is the ability

to do

can be which at a

given rate is

Energy Graphic Organizer

Kinetic energy

Energy

Potential

energy

Elastic

Work Joules

Gravitational Power