Enduring Understanding: For work to be accomplished, some type of energy is needed? Essential Question: What are the different types of energy? Essential Question: What are the social and economic impacts of energy use?

- the force applied to the object times the displacement travelled while that force is applied. work = force x displacement W = Fd

SI unit for work is the Joule (J) Example: A force of 100 N is used to push a stalled car 20 m across a parking lot. How much work was done on the car?

F = 100 N d = 20 m W = 100 N x 20 m = 2000 J The Joule is a derived unit. That means that forces must be in Newtons and distances must be in meters.

James Prescott Joule

Name another derived unit that we have used. The Newton (N) What are the base units used to derive the Newton and all of our derived units? Mass (kg) Distance (m) Time (s) Recall: F=ma

To calculate work, the force and displacement the object is moved must be parallel.

When you carry something up a staircase, you supply a force in the upward direction. So, the direction that matters is the upward or vertical direction.

The horizontal distance does not matter because there is no force in that direction.

Direction Matters If force and distance are in the same direction, the work done is positive (+). Same, + If force and distance are in opposite directions, the work done is negative (-). Opposite, -

Zero Work is done if - force and distance are perpendicular - the object doesn’t move (zero distance) - no force is applied A man carrying books A man pushing a wall. walking forward.

+, -, or 0 work 1. A football player carries a football across a field. 2. A boy pulls his wagon down the sidewalk. 3. Tori carries a box up a flight of stairs. 4. Tori carries a box down a flight of stairs. 5. A waitress carries a tray of food across a room. 6. Zach holds a heavy barbell. 7. Steve pushes on a closed door. 8. Friction acts on a sled moving down a hill.

The force required to lift an object is the object’s weight. remember that weight = mg

A person is carrying a 10 N object up a staircase which is 7.5 m in the horizontal direction and 15 m in the vertical direction. How much work was done on the object? Work = Force x Distance Work = 10 N x 15 m Work = 150 J

Sometimes the force is applied at an angle. Only the horizontal (x) component of the force is parallel to the displacement. To find that component use cosine of the angle. W = Fd cos 

cos 0 = 1 cos 180 = -1 cos 90 = 0

How much work is done on a 500 kg object if it is raised 10 m? Since the force is the weight, Force = 500 kg x 9.8 m/s 2 = 4900 N Work = Fd Work = 4900 N x 10 m Work = 4.9 x 10 4 J

-the rate at which work is done -SI Unit is Watt (W)

A 250 N force is used to move a mass 30 m in 40 s. How much work was done to the mass? 7500 J How much power was used? P = 7500 J / 40 s W Watts are derived from Joules and seconds.

Give an example that you know of where Watts are used to measure Power.

James Watt Steam Engine 1763

Steamboats How did the steam engine change the world?

Cultural Impact

Beyond being the battle of one man versus one machine, what is the significance of the story of John Henry? Give other examples of machines replacing people in the work force.

A 40 kg mass is lifted 20 m in 15 s. How much power was used? Work = 7.84 x 10 3 J Power = W