POWER

POWER

By Lecar Maghanoy

Thornton High School

​Learning objectives

• Explain how Work, Power and Force are related.

• Calculate for Power​

​WHAT IS POWER?

• Often people are not concerned about getting WORK done.

• They want it done fast, and that requires power.

• Power, like work has a precise meaning in Science.

Power is the rate of doing work.

• Doing work at a faster rate requires more power.

• To increase power, you can increase the amount of work done in a given time, or you can do a given amount of work in less time.

​Snow blower

​Power is the rate of doing work.

​

Because the snow blower can remove more snow in less time, it requires more power than handling shoveling does.

• This is an example of what a difference in power means when performing a task.

• Work is required to move a snow from one location to another.​

• A person using a shovel and a person using a snow blower can both do the work needed to remove the snow.

• Clearly, the snow blower can do more work in less time means that it has more power.​

Multiple Choice

Which of the following shows greater Power?

Multiple Choice

TRUE OR FALSE: To increase power, you can increase the amount of work done in a given time, or you can do a given amount of work in less time.

• TRUE

• FALSE

​Truck pushing a snowplow

Snow blower

​You may noticed that the size of the engine used by a machine is often an indication of its Power.

​For example, compare the snow blower's small engine with the engine used by a truck pushing a snowplow.

​

The truck's powerful engine allows it to remove snow at a very fast rate. ​

​calculating power

​You can calculate power by dividing the amount of work done by the time needed to do the work.

• Work is in JOULES (J)

• Time is in SECONDS (s)

• The SI unit of power is the Watt (W)

• 1 Watt = 1 joule per second (J/s)​

Example: 40-watt light bulb requires 40 joules each second that it is lit.​

​SI Units are

Multiple Choice

What is the Unit for Work?

• Seconds

• Meters

• Joules

• Force

Multiple Choice

What is the Unit for time?

• Seconds

• Newton

• Meter

• Watt

Multiple Choice

What is the SI unit for power?

• Force

• Watt

• Newton

• Joule

Multiple Choice

What is the equivalent for 1 watt?

• 1 Joule per second

• 1 Newton per meter

• 1 meter per second

• 1 watt per second

Math Skills

Solving for Power

What information are you given?

Force = 72 N

Time = 2.0 seconds

Distance = 1.0 meters​

​

​

​1. Read and Understand

Calculating Power

​Problem: You exert a vertical force of 72 newtons to lift a box to a height of 1.0 meter in a time of 2.0 seconds. How much power is used to lift the box?

​2. Plan and Solve

Open Ended

​Practice #1:

Your family is moving to a new apartment. While lifting a box 1.5 m straight up to put it on a truck, you exert an upward force of 200 N for 1.0 seconds. How much power to do this?

Open Ended

Practice #2:

You lift a book from the floor to a bookshelf 1.0 m above the ground. How much power is used if the upward force is 15.0 N and you so the work in 2.0 s?

​James Watt and Horsepower

• Another common unit of power is the horsepower.

• 1 horsepower (hp) = 746 watts

• The horsepower was first defined by Scottish Scientist James Watt (1736-1819)

• Watt was looking for a way to compare the power outputs of steam engine he had designs.​

• Horses were a logical choice for comparison as they were the most commonly used source of power in the 1700s. ​

​GT-Mustang 500

• 760 horsepower How fast is 760 horsepower?

• The company says the 760-hp muscle car will rocket to 60 mph in 3.3. seconds on its way to a 10.7-second quarter-mile.​

Multiple Choice

The unit for Power was named after which Scientist?

• James Watt

• John Watts

• Carl horsepower

• Isaac Newton

Multiple Choice

How many watts is 1 horsepower?

• 600 watts

• 1000 watts

• 546 watts

• 746 watts

Multiple Choice

Why horses are being used as comparison to Power of an engine?

• They are fast and strong

• Commonly used source of power before

• They are good followers to an experiment

• All of these

Poll

POLL: How well do you understand the relationship of Work and Power?

• Very Well

• Pretty Well

• Not Very Well

Open Ended

Exit Ticket: What is one take away you got from today’s lesson?

With great power comes with great responsibility