Unit: Three   Topic:  E
(Please Listen to Narration or read the Paragraphs below )

E1. Kinetic energy, introduction.

Kinetic energy is the energy a body possesses because it is in motion. For example, the potential energy had by a book on a table is converted to kinetic energy (motion) when it falls. The book lying flat on the floor does not have this same potential or kinetic energy.

E2. Kinetic energy, effect on driving.

As you increase your driving speed, both your body and your vehicle acquire kinetic energy which eventually must be: (a) absorbed by your brakes, engine compression forces, or other friction in a controlled stop, or (b) absorbed by your body, your vehicle's body, and the objects you hit if you are involved in a crash.

The kinetic energy of your body while it is in motion, of loose objects in the car, and of the car itself, all increase with weight and the square of your speed so that: (a) if you increase your speed from 10 MPH to 20 MPH, you are dealing with four times the amount of kinetic energy, and (b) if you increase you speed from 10 MPH to 50 MPH you have to deal with 25 times the amount of kinetic energy. The kinetic energy of your moving vehicle determines your ability to stop the car. In addition to the distance traveled due to your reaction time, your stopping distance will be (a) five times further if you increase your speed from 10 MPH to 20 MPH, and (b) 25 times further if you increase your speed from 10 MPH to 50 MPH.

Gravity decreases your kinetic energy when you are driving uphill and increases it when you are driving downhill. Therefore, the force of gravity will make it (a) easier to stop your car if you are going uphill, and (b) more difficult to stop your car if you are going downhill.

Braking to a stop converts kinetic energy into heat energy in your brakes through friction.  If you and your vehicle are involved in a collision, the kinetic energy is still converted into heat through friction, but not in your brakes (ouch!).