Lesson 8 Work and the Motor

Objectives Define “work” Describe the units of measure for work Use force and distance measurements to calculate work Compare the work done by different forces Compare the force exerted by a motor that is connected to three batteries in series with the force needed to lift a small sled.

Getting started Discuss the meaning of the word “work”. List some examples of work being done. Read “The Meaning Of Work”. Did your exampes match the scientific meaning of work? L 8

Getting Started Con’t Newton-meters Review how to calculate work and what the units of measure for work are. Work – when a force acts on an object and it moves some distance. Calculation: WORK = Force (N) x Distance (m) Units of measure: Newton-meters

Getting Started 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

Answer to problem Work = Force x Distance W = ? F = 12 N D = 5 m W = 12 N x 5 m = 60 N-m L 8

Problem 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 Work = Force x Distance W = ? F = 12 N D = 0.80 m W = 25 N x 0.80 m = 20.0 N-m L 8

1. What force are you working against when you lift a backpack? Questions about work 1. What force are you working against when you lift a backpack? L 8.1b Work ???

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

B. A tow truck is pulling a car slowly along the street. L8.1b Work ???

C. A student is studying for a mathematics exam. Work ??? L 8-1b

D. A student is pushing a grocery cart around a store. L 8.1b Work ???

E. Another student is standing in line holding a 12-N bag of potatoes. L 8.1b Work ???

F. A student pushes against the school building. Work ???

Vocabulary – Lesson 8 Work involves a force applied across a distance. Work: What happens when an object changes its position by moving in the direction of the force that is being applied is Work = force x distance (w = fd) Work involves a force applied across a distance. The metric unit of work is the newton-meter (N-m). A newton-meter is also a joule (J). James Joule – described the relationship between work and energy.

Vocabulary – Lesson 8 effort force: the force exerted by a person or motor when using a machine to lift a load. (In lab, this is the force is applied to lift the sled). effort distance. the distance over which the effort force acts in a simple machine. (In lab, this is the distance the sled moves).

Vocabulary – Lesson 8 Ampere (amp) :Electric current flows through the wire. The unit used to describe how much electric current flows through a wire is the ampere The ampere is named for Andre Ampere Volts: Measures the electric potential of a battery The volt is named for Alessandra Volta

Vocabulary Lesson 8 OUTPUT WORK: The work done on a load by a machine or motor. Load force x Load Distance = Output work INPUT WORK: The work done by the effort force in a simple machine or motor. Effort force x Effort distance = Input work

Notes Work is done on an object when a force acts on an object that moves through some distance. Work is equal to the force that pushes or pulls on the object multiplied by the distance the object moves W = F x D Work = Force x Distance

Notes If the object does not move any distance, no work has been done. Work is measured in units of Newton-meters. Force (N) x Distance (m) = Nm Work can also be measured in Joules One Newton-meter is equal to One Joule

Lesson 8 QUESTION

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 _________________. Hypothesis

Lesson 8 Materials 1. 2. 3. Procedure

Lesson 8 Results / Data / Observations

Inquiry 8.1 Calculating the Work Done on Different Surfaces

Inquiry 8.2 Work to Lift 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:______________ Work to raise six washers: Work = ______ x _______ = _______ 5. Your estimate of sled’s weight: _______ Sled’s actual weight: _________ L 8-2

WORK Work to lift sled 10.0 cm. (0.10 m): Work = _________ x ______ = _______ WORK L 8-2

Lesson 8 Conclusion