1. Unit B 1.4 Work and Energy

2. Force Defined as a push or a pull on an object Measured in Newtons Force (N) = mass (kg) x acceleration (m/s 2 ) Kg*m/s 2 = N

3. Work Force moving an object through a distance Measured in Joules (J) Work (J) = force (N) x distance (m) Three conditions necessary for work to be done on an object – Must be movement – Must be a force – Force and the distance an object travels must be in the same direction

4. When coasting on a bicycle, is work being done? – No, the rider is traveling over a distance, but no force is being applied A waiter carrying a tray can be strenuous while walking, but is work being done. – When the tray is lifted work is being done, but when walking no work is being done in regards to the tray.

5. Example A weightlifter lifts a barbell a vertical distance of 2.40m. If the average force required to lift the barbell is 2.00 x 10 3 N, how much work is done by the weightlifter on the barbell. W = F x d = (2.00 x 10 3 N)(2.40m) = 4.80 x 10 3 J Practice Problems 18 and 19 p. 160

6. Energy The ability to do work Work and energy are the same

7. Example A weightlifter does 4.80 x 10 3 J of work lifting a barbell. How much energy is gained by the barbell? Since E = W And W = 4.80 x 10 3 J Then E = 4.80 x 10 3 J Homework: read Science 10 p. 155 – 161, Check and Reflect 1-9