P H Y S I C S   

Introduction to Work, Power & Kinetic Energy

What is Work?

What do you think of when you think of work?

Work

Work is done when a force acts parallel to the direction of the displacement

Fo

rce

Displacement

Dis

pla

cem

ent

Force

Work

Work is done when a force acts parallel to the direction of the displacement

Air Resistance

Force

Displacement

Dis

pla

cem

ent

Friction Force

Work or Not?

Man holds out heavy concrete block at arm’s length for 10 minutes

Student pushes car down street Women holds up a large box over-head while

walking down the hall way Child pushes a cart along the side walk

WORK

WORK

NOT WORK

NOT WORK

What is kinetic energy?

What do you think of when you think of kinetic energy?

Kinetic Energy

Any moving object has kinetic energy Amount depends on

1) velocity

2) mass

Kinetic Energy Equation

KE kinetic energy (J)

m mass (kg)

v velocity (m/s)

Note:

Kinetic Energy

Work-Energy Theorem

Work done on an object is equal to its change in kinetic energy

W = ∆KEW work (J)

∆KE change in kinetic energy (J)

Note:

Work-Energy Theorem

+W increases KE

WORK

Formula for Work

W = f * d

W Work (J) f Force (N) d Displacement (m)

What is power?

What makes something powerful?

Power

The rate at which work is done

Work vs. Power

Power accounts for “how fast” work is done

A B

Power Equation

Unit:

P power (W) W work (J) t time (s)

Power Equation

Another variation derived from :

P power (W) F force (N) v velocity (m/s)

Household Appliances 60W light bulb - 60W Toaster : 800-1500W Microwave : 600-1500W Dishwasher : 1200-1500W Washing Machine : 500W Vacuum Cleaner : 200-700W Clothes dryer : 4000W Ceiling Fan : 10-50W Hair Blow dryer : 1000W Laptop Computer : 20-50W Desktop Computer : 80-150W Cell Phone Charger: 3-5W iPod/iPad Charger: 10W

Time to explore Power

What do we need to know to calculate power?

What is your force? So if 1lb=2.2kg how much mass do

you have? How can we calculate velocity?

On a sheet of paper

Calculate your Fg. Now let’s go to the stairs and see who

can generate the most power. When we get back calculate your

power. This paper is your exit slip. You can’t leave until it’s done.