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?

work = force x distance W = Fd SI unit is Joules (J)

James Prescott Joule 1818-1889

Example: A force of 15 N to push a stalled car 35 m across a parking lot. How much work was done on the car?

F = 15 N d = 35 m W = 15 N x 35 m = 525 J The Joule is a derived unit. That means that forces must be in Newtons and distances must be in meters.

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) Example: f=ma

In lifting an object, the force required is the object’s weight. remember that weight = mg

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/s2 = 4900 N Work = Fd Work = 4900 N x 10 m Work = 4.9 x 104 J

Scientific Notation Put 1250 in scientific notation. 1.25 x 103 What is 3.75 x 105 in long form? 375,000

To calculate work, the force and the distance the object is moved must be in the same direction. 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.

A person is carrying a 10 N object up a staircase which is 7 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

Power P = W/t Power is defined as the rate at which work is done SI unit is Watt (W) P = W/t

A 250 N force is used to move a mass 30 m in 40 s. How much work was done to the mass? 7.50 x 103 J How much power was used? P = 7.50 x 103 J / 40 s 187.5 W W stands for Watts. Watts are derived from Joules and seconds.

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

James Watt 1736-1819 Steam Engine 1763

How did the steam engine change the world? Steamboats

Cultural Impact

A 40 kg mass is lifted 20 m in 15 s. How much power was used? Work = 7.84 x 103 J Power = 522.7 W