Work

Work

Physics

​Work and Energy

​- Energy can change from one form to another, but the total amount of energy in the universe stays the same.

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​- Work and energy in everyday life:

​ - Get up in the morning and 'go to work'

​ - Hiking up a mountain we 'work up a sweat'

​ - Eat lunch and get 'energy'

​- In Physics, WORK (W) is defined as force times the distance moved

​ - SI unit: newton-meter (N*m) = joule (J)

- work = force X distance

​ - W = Fd

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​Work depends on Force and distance

​- In the simplest case, work is done when a force is applied to an object and the object moves in the direction of the applied force.

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​- If you push a box with a force F through a distance d, then the work you do is W = F*d

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​- Newtons times distance

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​- N * m

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​- 1 J = amount of energy needed to lift an apple 1 meter

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​Work is measured with a unit called the joule

​The angle of the force affects the work done

​- Only the component of the force in the direction of the displacement does work.

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​- W = Fd cos θ

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​Work

​- Work is zero if the distance moved is zero

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​- Work can be positive, negative, or zero

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​- The work done by separate forces can be summed

Open Ended

How is work calculated when force and displacement are in the same direction?

Open Ended

Give two examples of (a) positive work done by a frictional force and (b) negative work done by a frictional force.

Open Ended

A child in a tree house uses a rope attached to a basket to lift a 22-N dog upward through a distance of 4.7 m in to the house. How much work does the child do in lifting the dog??

Open Ended

To move a suitcase up to the check-in stand at an airport, a student pushes with a horizontal force through a distance of .95m. if the work done by the student is 32 J, what is the magnitude of the force he exerts?

Open Ended

A farmhand pushes a bale of hay 3.9 m across the floor of a barn. She exerts a force of 88 N at an angle of 25 degrees below the horizontal. How much work has she done?

Open Ended

The coefficient of kinetic friction between a large box and the floor is .21. A person pushes horizontally on the box with a force of 160 N for a distance of 2.3 m. If the mass of the box is 72 kg, what is the total work done on the box?