Chapter 12:Energy & Work Unit

Integrated Science I

Kinetic energy is the energy of motion

Measured in Joules (J)

Depends on two variables◦ The amount of mass of the object◦ The velocity of the object

Kinetic Energy

K.E. = ½ m x v2

K.E. = Kinetic Energy (J)m = mass (kg)

v = velocity (m/s)

How to Calculate K.E.:

Determine the kinetic energy of a 625-kg roller coaster car that is moving with a speed of 18.3 m/s.◦ Equation: KE = ½ m x v2

◦ Substitute: KE = ½ (625 kg) x (18.3 m/s)2

◦ Simplify: KE = (312 kg) x (334.9 m/s)◦ Answer: KE = 104,468.7 J

Kinetic Energy Practice Problem

Gravitational potential energy is energy not moving yet

Stored in an object as the result of it being above the ground

GPE is measured in Joules (J) Objects have more GPE when…

◦They have more mass◦They are higher off the ground

Gravitational Potential Energy (GPE)

G.P.E. = m x g x h

GPE = gravitational potential energy (J)

m = mass (kg)g = gravity (10 m/s2)

h = height of object (m)

How to Calculate G.P.E.:

A plate of spaghetti has potential energy because it is hanging off the counter. The plate of spaghetti has a mass of 1.3 kg and is sitting on a 1.2 meter high counter. How much potential energy does the spaghetti have?

◦ Equation: PE = M x H x 9.8 m/s2

◦ Substitution: PE = (1.3 kg) x (1.2 m) x (10 m/s2)◦ Answer: GPE = 15.6 J

Potential Energy Practice Problem!!

Energy cannot be created or destroyed This means energy is never lost – it is only

transformed. Most common type of energy

transformation:◦ Friction: if friction was not present, the total

amount of energy in a system would always be the same!!!⚫Instead – kinetic energy is transformed to thermal

energy

Law of Conservation of Energy

Work requires, 1) movement and 2) movement in same direction as the force

Press your hand against the desk as hard as you can. Are you doing any work?◦ No! ☹ Why not?

⚫Work is the transfer of energy that occurs when a force makes an object move.

⚫You did not make the object move, therefore you did not do any work.

Work is the Transfer of Energy!!

Force and movement MUST BE IN THE SAME DIRECTION!!

W = f x dw = work (J)f = force (N)

d = distance (m)

How to Calculate Work:

Work Practice Problem!!! You move a 100-kg roller coaster car 30

meters because it broke down. This requires a force of 70 N. How much work, in joules, was done while moving the roller coaster car?

◦Equation: W = f x d◦Substitution: W = (70N) x (30m)◦Answer: W = 2,100 J