Sing-A-Long

http://www.youtube.com/watch?v=vl4g7T5gw1M
Work and Power

Work = Force x Distance
 W=Fd

(Unit is Nm or JOULES)
Power = Work / Time
P
= W/T (Unit is WATTS)
 How fast you do work
What is energy?

ENERGY is the ability to do work

Measured in Joules (J) = Nm
Forms of energy

Energy can exist in many different forms and
changes from one form to another
Kinetic Energy


KINETIC ENERGY is the energy of motion
Depends on mass and velocity
Kinetic Energy
Which has a higher maximum
kinetic energy, the first car or the
camaro? Why?
The camaro has more KE
because it has a higher velocity.
Kinetic Energy
Which would hurt more, getting hit by a 15 foot wave
or a 2 foot wave? Why?
The bigger wave would hurt
more because even though they
travel at the same speed, the
bigger wave has more mass.
Kinetic Energy

Formula:
KE =
mass (in kg)
2
½mv
velocity (in m/s)
Kinetic Energy

The bird has a mass of 2 kg. It is flying at a
speed of 5 m/s. Find its kinetic energy.
KE = ?
m = 2 kg
v = 5 m/s
KE = ½mv2
KE = ½(2 kg)(5 m/s)2
= 25 J
Work it Out with a Partner!
A baseball has a mass of
about 0.15 kg. A pitcher
throws the ball at 40 m/s
(this is about 90 mph).
How much kinetic energy
does the ball have?
Potential Energy



An object with POTENTIAL ENERGY has the ability
(or potential) to move or change
Sometimes called “energy of position” or “stored
energy”
There are 3 types of potential energy:
 Gravitational
Potential Energy
 Elastic Potential Energy
 Chemical Potential Energy
Gravitational Potential Energy


Potential Energy due to an object’s position
Formula:
PE = mgh
mass (in kg)
acceleration of
gravity (9.8 m/s2)
height (in
meters)
Gravitational Potential Energy
•The person has
more potential
energy at the top
of the stairs than at
the bottom.
Gravitational Potential Energy
Where does the egg have more potential
energy? Why?
Work it Out with a Partner
A cat is on the top
branch of a tree. The
tree is 15 meters
high and the cat has
a mass of 5 kg. How
much potential
energy does the cat
have?
Elastic Potential Energy

Potential energy due compression or expansion of
an elastic object
Chemical Potential Energy

Potential energy stored within the chemical bonds of
an object
Practice Problems
1. 0.20 kg apple hangs on a tree and has 14 J of potential energy.
How high off the ground is the apple?
2. A student eats a candy bar that can provide 1.57 x 106J of energy.
If the student has a mass of 81.8 kg, how high will he have to climb a
ladder to offset completely the energy contained in the candy bar?
3. The diagram below represents a 155 N box on a ramp. A force is
applied that will cause the box to slide from point A to point B.
What is the total amount of gravitational potential energy gained by
the box?
Graphic Organizer Summary
Joules (J)
PE= mgh
Potential
Kinetic
Chemical
Gravitational
KE = ½ mv2
Elastic
mass
mass
velocity
position