Lesson 8

Work

• Work – when a force acts on an object and it moves some distance.

WORK = Force (N) x Distance (m)

L 8

WORK

Alice pulls a sled with a force of 12 N. She pulls the sled through a distance of 5 m. How much work does Alice do on the sled?

L 8

WORK

Work = force x distance

Work = 12 N x 5 m = 60 N-m

L 8

WORK

Michael lifts his book bag, which weighs 25 N, from the floor to a desktop that is 0.80 m above the floor. How much work does Michael do on the bag?

L 8

WORK

Force x Distance = WORK

25 N x 0.80 m = 20.0 N-m

L 8

Inquiry 8.1Calculating the Work Done

on Different Surfaces

SURFACE EFFORT FORCE (N)

EFFORT DISTANCE (m)

WORK DONE (N-m)

TABLETOP

WAXED PAPER

PAPER TOWEL

FINE

SANDPAPER

COARSE

SANDPAPER

L 8

• 1. What force are you working against when you lift a backpack?

• L 8.1b

• 2. In which of the following cases is work, as defined by scientists, being done?

• A. Someone tries to move a piano, but the piano won’t budge.

• L 8.1b

• B. A tow truck is pulling a car slowly along the street.

• L8.1b

• C. A student is studying for a mathematics exam.

L 8-1b

• D. A student is pushing a grocery cart around a store.

• L 8.1b

• E. Another student is standing in line holding a 12-N bag of potatoes.

• L 8.1b

• F. A student pushes against the school building.

• L 8.1b

Lesson 8

Question – Lesson 8

• Is the motor capable of doing enough work to lift the sled to a distance of .10 m?

• Lesson 8

• If _________________,then __________ because _________________.

• Lesson 8

• Materials

• 1.

• 2.

• 3.

• Lesson 8

Lifting a Load

• 1. Motor force with three batteries in series: _________________

• 2. Work done by a motor when it lifts a load 10.0 cm. (0.10 m)

• Work = _______ x _______ = ______

L 8-2

3. Weight of six washers:______________

4. Work to raise six washers:

Work = ______ x _______ = _______

5. Your estimate of sled’s weight: _______

6. Sled’s actual weight: _________

L 8-2

7. Work to lift sled 10.0 cm. (0.10 m):

Work = _________ x ______ = _______

L 8-2

• Lesson 8

Vocabulary – Lesson 8

• What happens when an object changes its position by moving in the direction of the force that is being applied is(62) work.

• Work = force x distance (w = fd)• Work involves a force applied across a distance.

• The metric unit of work is the(63) newton-meter (N-m).

• A newton-meter is also a(64) joule (J).

• James Joule – described the relationship between work and energy.

L8

Vocabulary – Lesson 8

• A force is applied to lift the sled. This is the

(65) effort force.

• The distance the sled moves is the

(66) effort distance.

Vocabulary – Lesson 8

• Electric current flows through the wire. The unit used to describe how much electric current flows through a wire is the

(67) ampere (amp).• Andre Ampere

• The electric potential of a battery is measured in

(68) volts.• Alessandra Volta