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.
Pushing a 1-kilogram object with a force of one newton for a distance of one meter uses one joule of 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 massan 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
** 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. 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
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