UNIT 7Energy & Work

Energy• Energy – the ability to do work

• (the ability to cause a change)

Mechanical Energy

• Two types of mechanical energy• Potential Energy - energy of position• Kinetic energy – energy of motion

Kinetic Energy

• Kinetic energy – energy of motion

Kinetic energy• What if the mass is doubled?

• What happens to the kinetic energy if the velocity is doubled?

Potential Energy

•Potential energy – energy of position/location•Chemical potential •Elastic potential•Gravitational potential•Electric potential•Nuclear potential

Gravitational Potential Energy

Pe

Gravitational Potential Energy• What happens to the gravitational potential energy if the

mass is doubled?

• What if the height is doubled?

Conservation of EnergyLaw of Conservation of Energy

Energy cannot be created or destroyed. It can be transformed from one form to another, but the total amount of energy never changes.

Pendulum

Starts out not moving

Potential Kinetic

Starts out not moving

Potential Kinetic

Potential Kinetic

Potential Kinetic

Potential Kinetic

Potential Kinetic

Total energy = kinetic + potential

Potential Kinetic Potential Kinetic Potential Kinetic

Potential Kinetic Potential Kinetic

Total energy of the pendulum is conserved

Conservation of EnergyLaw of Conservation of Energy

Energy cannot be created or destroyed. It can be transformed from one form to another, but the total amount of energy never changes.

- What are some examples of transformation of energy?

Different starting conditions

• What if I start the pendulum higher?

Potential Kinetic Potential Kinetic

Different starting conditions

• What if I start the pendulum higher?

Potential Kinetic Potential Kinetic

Different starting conditions

• What if I push the pendulum instead of just letting go of it?

Potential Kinetic

Different starting conditions

• What if I push the pendulum instead of just letting go of it?

Potential Kinetic

Rollercoaster

What would the energy bar chart look like?

Potential Kinetic

What would the energy bar chart look like?

Potential Kinetic

What would the energy bar chart look like?

Potential Kinetic

When does a pendulum have the most Total Energy ?

Energy

• Energy initial = Energy final• Scenario: A boulder resting on a hilltop• What kind of energy does the boulder have at the top of

the hill?• What will happen to that energy as the boulder rolls down

the hill? Why?• What kind of energy does the boulder have as it rolls down

the hill?• What will happen to this energy as the boulder rolls down

the hill? Why?• What would happen to the two types of energy mentioned

if the hill on which the boulder sits was much taller?

Work• Two things must occur for work to be done.

1- a force must be applied2- something must move as a result of that force

• Work = force x distanceOr W=fd unit= Nm or J (joules)

Power• Power = rate at which work is done.

P= W

t

(unit is 1 J/s OR 1 W (watts) )

(i.e. 40 W = 40 J/s)

1 horsepower = 746 Watts

Making Work Easier

•A device that makes work easier is a machine.

•They make work easier by increasing the force applied to an object

• examples: crowbar (opening a box) a ramp (raising a box) a screwdriver (increase the force applied to a screw)

Simple Machines-Six types of simple machines:• Lever a bar that is free to pivot or turn• Pulley a grooved wheel with a rope , chain or cable running along a groove

• Wheel and Axle consisting of a shaft or axle attached to the center of a large wheel, such that they rotate together (screw drivers, doorknobs, faucet handles

• Inclined plane a sloping surface such as a ramp that reduces the amount of force required to do work

• Screw an inclined plain wrapped in spiral around a cylindrical post

• Wedge an inclined plane moves through an object or material (an axe blade or knife

Conservation of energy• When you do work on a machine your transferring energy to the machine.

• The force that is applied to the machine is called the input force And the force applied by the machine is called the output force.

• Meaning work in is equal to work out

Win = Wout

Fin Din = Fout Dout

Mechanical Advantage