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Work in ScienceWork in Science

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What is work?What is work?

In science, the word In science, the word workwork has a has a different meaning than you may be different meaning than you may be familiar with.familiar with.

The scientific definition of work is: The scientific definition of work is: using a force to move an object a using a force to move an object a distance (when both the force and distance (when both the force and the motion of the object are in the the motion of the object are in the same direction.)same direction.)

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Work or Not?Work or Not?

According to the According to the scientific definition, scientific definition, what is work and what is work and what is not?what is not? a teacher lecturing a teacher lecturing

to her classto her class a mouse pushing a a mouse pushing a

piece of cheese piece of cheese with its nose across with its nose across the floorthe floor

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Work or Not?Work or Not?

According to the According to the scientific definition, scientific definition, what is work and what is work and what is not?what is not? a teacher lecturing a teacher lecturing

to her classto her class a mouse pushing a a mouse pushing a

piece of cheese piece of cheese with its nose across with its nose across the floorthe floor

55

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What’s work?What’s work? A scientist delivers a speech to an A scientist delivers a speech to an

audience of his peers. audience of his peers. A body builder lifts 350 pounds A body builder lifts 350 pounds

above his head. above his head. A mother carries her baby from room A mother carries her baby from room

to room. to room. A father pushes a baby in a carriage.A father pushes a baby in a carriage. A woman carries a 20 kg grocery bag A woman carries a 20 kg grocery bag

to her car? to her car?

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What’s work?What’s work? A scientist delivers a speech to an A scientist delivers a speech to an

audience of his peers. audience of his peers. NoNo A body builder lifts 350 pounds A body builder lifts 350 pounds

above his head. above his head. YesYes A mother carries her baby from room A mother carries her baby from room

to room. to room. NoNo A father pushes a baby in a carriage. A father pushes a baby in a carriage. YesYes A woman carries a 20 km grocery A woman carries a 20 km grocery

bag to her car? bag to her car? NoNo

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Formula for workFormula for work

Work = Force x DistanceWork = Force x Distance

The unit of force is newtonsThe unit of force is newtons The unit of distance is metersThe unit of distance is meters The unit of work is newton-metersThe unit of work is newton-meters One newton-meter is equal to one jouleOne newton-meter is equal to one joule So, the unit of work is a So, the unit of work is a joulejoule

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W=FDW=FD

Work = Force x Work = Force x DistanceDistance

Calculate: If a Calculate: If a man pushes a man pushes a concrete block 10 concrete block 10 meters with a meters with a force of 20 N, force of 20 N, how much work how much work has he done?has he done?

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W=FDW=FD

Work = Force x Work = Force x DistanceDistance

Calculate: If a Calculate: If a man pushes a man pushes a concrete block 10 concrete block 10 meters with a meters with a force of 20 N, how force of 20 N, how much work has he much work has he done? done? 200 joules200 joules(W = 20N x 10m)(W = 20N x 10m)

WorkWork

Work happens when a Work happens when a force moves an object force moves an object over a distance.over a distance.

If the object does not If the object does not move, move, NONO work is done! work is done!

(Scientifically speaking)(Scientifically speaking)

WorkWork

Stand and hold your arms out in Stand and hold your arms out in front of you at waist level, palms up. front of you at waist level, palms up.

Have your partner stack two books Have your partner stack two books on your hands, one on each hand. on your hands, one on each hand.

Lift the books to about shoulder Lift the books to about shoulder level, then lower them. level, then lower them.

Now try raising them overhead Now try raising them overhead

WorkWork

When your hands are When your hands are overhead, are you overhead, are you working harder than working harder than when you raised them when you raised them to shoulder level? to shoulder level?

Describe your Describe your observations to your observations to your partner.partner.

WorkWork

Have your partner put two more books on Have your partner put two more books on each of your hands, so you’re holding four each of your hands, so you’re holding four books. Try to raise them to shoulder level. books. Try to raise them to shoulder level.

Are you pushing harder (using more force) Are you pushing harder (using more force) than when you were holding only two than when you were holding only two books? books?

Describe your observations to your Describe your observations to your partner.partner.

WorkWork

Hold the four books at shoulder level Hold the four books at shoulder level until your arms get tired. Are you until your arms get tired. Are you exerting force? exerting force?

Do you think you are doing work in Do you think you are doing work in these situations? What is the work these situations? What is the work being done on?being done on?

Describe your observations to your Describe your observations to your partner.partner.

WorkWork

You have 5 objects You have 5 objects on your table.on your table.

Use the spring scale Use the spring scale and a meter stick to and a meter stick to find the force needed find the force needed to move each object to move each object one meter.one meter.