Transcript What is energy?

What is energy?
Energy measures the ability for things to
change themselves or to cause change in other
things.
A joule (J) is the S.I. unit of measurement for energy.
Pushing a 1-kilogram object with a force of one newton
for a distance of one meter uses one joule of energy
1. Kinetic Energy
An object that moves has kinetic energy (when you
walk, run, jump -- you have K.E.)
How much Kinetic Energy an object has depends on
2 things:
a. The mass of the object
b. The speed its moving at
The more speed an object has the more KE it has.
Ex: a fastball has more KE than a slow curve ball.
The more mass an object has the more KE it has.
Ex: Think of a tennis ball rolling across your foot
…compared to a bowling ball rolling across your foot
The formula used to find kinetic energy is:
Ek = mass x velocity (speed)2
2
** Notice the velocity (speed) is squared.
This means if you go twice as fast, your energy increases by
four times (22=4)
SAMPLE PROBLEM: Find the kinetic energy of a 50 kg
swimmer, swimming at a speed of 4 m/sec. (Use 5 steps to
solve) YES -- 5 STEPS!!
1. Ek = mass x speed 2
2
2. Ek = 50 kg x (4m/sec) 2 ÷ 2
3. Ek = 50kg x 16 m2/sec2÷2
4. Ek = 800kg/m2/sec2 ÷2
5. Ek = 400 joules
2. Potential Energy - is "stored" energy or energy an
object has due to its position.
Ex: An archer gives potential energy to a
bow by pulling it back. The stored energy can be
used to send the arrow flying through the air.
•Potential energy associated with objects that can be
stretched (bow) or compressed (spring) is called elastic
potential energy.
•Potential energy that depends on height is called
gravitational potential energy.
Ex: A person standing on the edge of
an 3-meter cliff.
The formula for finding gravitational potential energy
(when the mass is in kilograms) is:
Ep= mass x acceleration due to gravity x height
SAMPLE PROBLEM: Find the potential energy of a 50 kg
diver on a 15 meter cliff.
Ep = mass x acceleration due to gravity x height
Ep = 50 kg x 9.8 m/sec2 x 15 meters
Ep = 7350 joules
When the mass (weight) is given in newtons you would use
the formula
Ep = mass x height