1 Work in Science

2 What is work?  In science, the word work has a different meaning than you may be familiar with.  The scientific definition of work is: using a force to move an object a distance (when both the force and the motion of the object are in the same direction.)

3 Work or Not?  According to the scientific definition, what is work and what is not? a teacher lecturing to her class a teacher lecturing to her class a mouse pushing a piece of cheese with its nose across the floor a mouse pushing a piece of cheese with its nose across the floor

4 Work or Not?  According to the scientific definition, what is work and what is not? a teacher lecturing to her class a teacher lecturing to her class a mouse pushing a piece of cheese with its nose across the floor a mouse pushing a piece of cheese with its nose across the floor

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6 What’s work?  A scientist delivers a speech to an audience of his peers.  A body builder lifts 350 pounds above his head.  A mother carries her baby from room to room.  A father pushes a baby in a carriage.  A woman carries a 20 kg grocery bag to her car?

7 What’s work?  A scientist delivers a speech to an audience of his peers. No  A body builder lifts 350 pounds above his head. Yes  A mother carries her baby from room to room. No  A father pushes a baby in a carriage. Yes  A woman carries a 20 km grocery bag to her car? No

8 Formula for work Work = Force x Distance  The unit of force is newtons  The unit of distance is meters  The unit of work is newton-meters  One newton-meter is equal to one joule  So, the unit of work is a joule

9 W=FD Work = Force x Distance Calculate: If a man pushes a concrete block 10 meters with a force of 20 N, how much work has he done?

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

Work  Work happens when a force moves an object over a distance.  If the object does not move, NO work is done!  (Scientifically speaking)

Work  Stand and hold your arms out in front of you at waist level, palms up.  Have your partner stack two books on your hands, one on each hand.  Lift the books to about shoulder level, then lower them.  Now try raising them overhead

Work  When your hands are overhead, are you working harder than when you raised them to shoulder level?  Describe your observations to your partner.

Work  Have your partner put two more books on each of your hands, so you’re holding four books. Try to raise them to shoulder level.  Are you pushing harder (using more force) than when you were holding only two books?  Describe your observations to your partner.

Work  Hold the four books at shoulder level until your arms get tired. Are you exerting force?  Do you think you are doing work in these situations? What is the work being done on?  Describe your observations to your partner.

Work  You have 5 objects on your table.  Use the spring scale and a meter stick to find the force needed to move each object one meter.