UNIT 7 Energy & 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 PePe

What happens to the gravitational potential energy if the mass is doubled? What if the height is doubled?

Conservation of Energy Law 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

PotentialKinetic Energy Starts out not moving

PotentialKinetic Energy

PotentialKinetic Energy

PotentialKinetic Energy

PotentialKinetic Energy

PotentialKinetic Energy

Total energy = kinetic + potential Potential Kinetic Energy PotentialKinetic Energy PotentialKinetic Energy PotentialKinetic Energy Potential Kinetic Energy Total energy of the pendulum is conserved

Conservation of Energy Law 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? PotentialKinetic Energy Potential Kinetic Energy

Different starting conditions What if I start the pendulum higher? PotentialKinetic Energy Potential Kinetic Energy

Different starting conditions What if I push the pendulum instead of just letting go of it? PotentialKinetic Energy

Different starting conditions What if I push the pendulum instead of just letting go of it? PotentialKinetic Energy

Rollercoaster

What would the energy bar chart look like?

Potential Kinetic Energy

What would the energy bar chart look like?

PotentialKinetic Energy

What would the energy bar chart look like?

Potential Kinetic Energy

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 applied 2- something must move as a result of that force Work = force x distance OrW=fdunit= 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 W in = W out F in D in = F out D out

Mechanical Advantage