physics work and energy

Preview

Section 1 Work

Section 2 Energy

Section 3 Conservation of Energy

Section 4 Power

Mr. Thompson's Physics Class

What do you think? List five examples of things you have done in the last year that

you would consider work. Based on these examples, how do you define work?

Mr. Thompson's Physics Class

Work In physics, work is the magnitude of the force (F) times the

magnitude of the displacement (d) in the same direction as the force.

W = Fd What are the SI units for work?

Force units (N) x distance units (m) N•m are also called joules (J).

How much work is 1 joule? Lift an apple weighing about 1 N from the floor to the

desk, a distance of about 1 m.

Mr. Thompson's Physics Class

Work In physics, work is the magnitude of the force (F) times the

magnitude of the displacement (d) in the same direction as the force.

W = Fd What are the SI units for work?

Force units (N) x distance units (m) N•m are also called joules (J).

How much work is 1 joule? Lift an apple weighing about 1 N from the floor to the

desk, a distance of about 1 m.

Mr. Thompson's Physics Class

Work and Energy Section 1

© Houghton Mifflin Harcourt Publishing Company

Work

• Pushing this car is work because F and d are in the same direction.

• Why aren’t the following tasks considered work?– A student holds a heavy chair at arm’s

length for several minutes.– A student carries a bucket of water along

a horizontal path while walking at a constant velocity.

Mr. Thompson's Physics Class

Work and Energy Section 1

© Houghton Mifflin Harcourt Publishing Company

WorkHow would you calculate the work in this case?What is the component of F in the direction of d?

• F cos

– If the angle is 90°, what is the component of F in the direction of d?

• F cos 90° = 0– If the angle is 0°, what is the

component of F in the direction of d?• F cos 0° = F

Mr. Thompson's Physics Class

Work

Mr. Thompson's Physics Class

Work is a Scalar Work can be

positive or negative but does not have a direction.

What is the angle between F and d in each case?

Mr. Thompson's Physics Class

Classroom Practice Problem A 20.0 kg suitcase is raised 3.0 m above a

platform. How much work is done on the suitcase?

Answer: 5.9 x 102 J or 590 J

Mr. Thompson's Physics Class

Now what do you think? Based on the physics definition, list

five examples of things you have done in the last year that you would consider work.

Mr. Thompson's Physics Class