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Energy
Chapter 4
Energy

Any and every change that occurs,
involves energy
Kinetic Energy
The energy a moving object has
because of its motion
 Kinetic energy of a moving object
depends on:
objects mass and its speed

Kinetic Energy Equation

Kinetic energy (in joules) = ½ mass
(kg) x [speed/velocity (in m/s)]²

KE = ½ mv²
Try It

A jogger with a mass of 50 kg is
moving at a speed of 3.0 m/s. What is
the joggers kinetic energy?
Potential Energy
Stored energy due to position
 Ex:
Rock on top of hill
Vase on edge of shelf
Ball ready to be dropped

Elastic Potential Energy
Energy stored by something that can
stretch or compress
 Ex:
Rubber band
Spring
Bouncy ball
Basket ball

Chemical Potential Energy
Energy stored in chemical bonds
between atoms
 Ex:
Carbon dioxide
Water

Gravitational Potential Energy

Energy stored by objects due to their
position above the Earth’s surface

GPE depends on objects mass and
height above the ground
GPE Equation

Gravitational potential energy (J) =
mass(kg) x accel. due to gravity(m/s²)
x height (m)
•
GPE = mgh
Try It

What is the gravitational potential
energy of a ceiling fan that has a mass
of 8.0kg and is 4.0 meters above the
ground
Conservation of Energy
“Energy is not created or destroyed.”
 Energy is only transformed or
transferred

PE can change to KE and back
 Ex: Roller Coaster

Roller Coaster
Mechanical Energy

The total amount of potential and kinetic
energy in a system
Ex:
mech. Energy = pot. Energy + kin. energy

Ch. 6 – Thermal Energy
Temperature – a measure of the
average kinetic energy of the particles
in the object
 Thermal Energy – the sum of the
kinetic and potential energy of all the
particles in an object


Temp. and Thermal Energy are related
Heat

Transfer of energy from object at
higher temperature to an object of
lower temperature
Hotter object to colder object
 Ex: Hand to ice, fire to hand

Specific Heat
The amount of heat that is needed to
raise the temperature of 1kg of a
material by 1◦C
 Measured in [J/(kg◦C)]


Temperature change depends on the
nature of the substance and amt of
heat added
Thermal Energy Equation

Change in thermal energy (J) =
mass (kg) x change in temp(◦C) x
specific heat
•
Q = m(Tf – Ti)C
Try It

A wooden block has a mass of 20.0
kg and specific heat of 1,700 J/(kg◦C).
Find the change in thermal energy of
the block as it warms from 20◦C to
30◦C.
3 Types of Energy Transfer
1.
2.
3.
Conduction
Convection
Radiation
Conduction

Heat transfer
between 2
touching objects
 Exs: Touching hot
metal, pot on stove
Convection

Heating a fluid
(liquid or gas)
 Exs: boiling water,
hot air balloon
 Hot gas/liquid rises
Radiation


Heat thru
electromagnetic waves
(microwave, sun, uv,
etc.)
Doesn’t need solid,
liquid, or gas to work
Types of Energy Transfer
Conductors & Insulators
Conductor – transfer heat well
 Exs: metal

Insulators – hinders heat transfer
 Exs: rubber, plastic, clothing

Conductor & Insulator

House Insulation insulator

Copper Wire Conductor