1. Journal 2/25/16 What is power? Make a list of all the things this means. Objective Tonight’s Homework To learn how we apply energy with a time factor p 333: 4 p 334: 8 Find wattage of 10 things

2. Power We said work is simply a measure of how we’re using energy to make stuff change. But there’s still a piece we’re missing. Compare the following: Driving to Grandma’s house… … or driving to Grandma’s house with a rocket engine strapped to the car.

3. Power Assuming you can control the car in both setups, what’s different between the two?

4. Power Assuming you can control the car in both setups, what’s different between the two? The second one will get you to Grandma’s much faster because it has more power. Power tells us how fast we do work. In the end, the same amount of work gets done, we just get it done way faster with more power.

5. Power The units for this will be fairly familiar, too. We measure power in “watts”. 1 Watt is when we’re using 1 Joule of energy every second. Your body puts out about 100 Watts of heat. A T.V. uses between 300 and 500 Watts. A microwave uses around 1,100 Watts. A washer uses around 5,000 Watts.

6. Equations EVSEVS P = W / t P: Power in Watts W: Work in Joules t: time in seconds This can tell us how much time it takes to do a certain amount of work, or it can tell us how much energy gets used over a certain amount of time. Power

7. Power Practice 1) Calculate the power of a force of 1 N moving a book 2 meters in 1 second. 2) Calculate how much power is used when a 20-N force pushes a cart 3.5 meters in 2 seconds.  Compare the power of 2 rockets. Rocket A travels 30,000 meters in 150 seconds with a thrust of 10,000 N. Rocket B travels 40,000 meters in 160 seconds with a thrust of 9,000 N. Which has the greater power? By how much? After finishing these, you have time for the rest of class for a grade check or to catch up on missing assignments. Part of your homework for tonight is to find the wattage of 10 things in your house. This is almost always listed in the label for the appliance or device.

8. Exit Question A typical car has somewhere around 100,000 watts of power. If it takes the car 1,800 seconds to burn a gallon of gas, how much energy is in 1 gallon of gas? 0.018 J 56 J 350,000 J 180,000,000 J Not enough information