Lesson 9 Objectives Calculate the power of a

Lesson 9

Objectives • Calculate the power of a motor • Investigate how the time it takes a motor to lift a load depends on the number of batteries connected in series to the motor • Investigate how a motor’s power depends on the number of batteries connected in series to the motor.

POWER Getting Started 1. How are work and energy related? Energy is the ability to do work How are work and power related? Power is the rate at which work is done L 9

POWER 2. How do you calculate power? POWER = WORK (Force x Distance) (N-m) TIME (s) • 3. What are the most commonly used units of measure for power? The common unit of power is the watt (W). 1 watt = 1 newton-meter second

POWER A girl pushes on a box at a steady pace with a force of 8. 0 N. She moves the box 3. 0 m in 5. 0 s. What is her power output? L 9

POWER Power = work = Newton-meter = watts time second Remember Work = Force x Distance Force = 8. 0 N Distance = 3. 0 m Time = 5 sec Power =8. 0 N x 3. 0 m 5 s = 4. 8 Watts L 9

POWER • A motor steadily lifts a load that weighs 5. 0 Newtons a distance of 1. 5 meters in 2. 0 seconds. What is the power output of the motor?

POWER Power = Force x distance time Force = 5. 0 N Distance = 1. 5 m Time = 2 sec Power = 5. 0 N x 1. 5 m 2 s = 3. 75 Watts •

QUESTION? ? ? • What factors might affect the time is takes a motor to lift a load?

ANSWER • How much force the motor has • How many batteries the motor has • How heavy a load the motor has to lift

Vocabulary – Lesson 9 • The rate at which work is done is (69) power. • work divided by time • measure of the rate at which energy transformations take place or the rate at which work is done • The unit used to measure power is the (70) watt (w). • 1 w = 1 joule per second • James Watt L 9

Vocabulary • Horsepower: Unit of Power in the English system at which work is done or at which energy transformations take place. • 1 horsepower = 750 W • Energy: Ability to do work

Notes • When work is done, energy is converted from one form to another. • Energy is the ability to do work, so any object that has energy, can do work.

Notes • Power is a measure of the rate at which work is done OR at which energy transformations take place. • Power = Work/Time • Power is measured in watts. • One Watt is = One joule of work/second • = One Newton-Meter/second

Notes • The kilo. Watt is a unit of measurement for very powerful devices. • 1 k. W = 1000 W • Electric companies use this unit to calculate kilowatt-hours, a unit that measures electric energy. • .