Work in the physics sense means to apply a force to an object over a certain distance. In turn, that work is transformed into kinetic energy. The kinetic energy is the energy of motion. Any object in motion had to be put into motion by some force; therefore, it turns out that the work done on the object equals the energy the object has after it is set into motion. Since kinetic energy depends on motion, it is directly related to the speed of the object. However, it is a square relationship. For example, if you double the speed of an object you actually quadruple the energy. If you triple your speed, your energy will be increased by a factor of nine!

This fact has important implications in gas consumption. Since doubling your speed increases your energy by four, the amount of work needed to attain and maintain that speed also increases by four. So, your car has to work four times harder to go 60 mph compared to 30 mph. Furthermore, your car has to work nine times harder to go 90 mph compared to 30 mph.

Unfortunately, once an object has energy, it requires work to bring the object to a stop. That can either be accomplished by using the breaks, or through a collision. Regardless of the method, the amount of work needed equals the object's energy. Consequently, the work done on stopping a car during a collision is directly related to the amount of damage sustained. So, a car will have four times the damage if it hits a tree at 60 mph as opposed to 30 mph. It is an exponential increase that becomes deadly in a hurry.

Seat belts and air bags are implements designed to help protect the person involved in an automobile accident. This brings in impulse and momentum. Momentum also depends on speed but is not a square relationship. So, doubling the speed also doubles the momentum of a moving object. Impulse involves the force required to start or stop a moving object over the amount of time the force is applied. For example, for a given momentum, if the stopping time is large, the stopping force will be small. This would be for the case of a car breaking for a long distance. However, if the car with the same momentum stops through an impact, and the impact time is small, the force will be large. Therefore, the goal is to increase the time of impact as much as possible to decrease the stopping force.

The relationship between energy and momentum provides some interesting insight into moving objects. They both depend on the mass of an object, and they depend on the speed. But, energy has a square relationship while momentum does not. The following example will illustrate this point. There are two cars with the same momentum. However, car A has half the mass as car B. As a result, car A has to have twice the speed in order to equal car B's momentum. Both cars hit a wall with the same exact impact time. This means the stopping force will be the same for both cars. The passengers did not have restraining devices, so they are stopped by the dash and windshield. Even though both cars hit the wall with the same exact force, car A will sustain four times the damage than that of car B. The people in car A will experience four times more pain than the people in car B. This fact has implications in not only automobile accidents, but in sports as well.

The learning outcomes of this unit span the content and the student's ability to think critically about the consequences and benefits of the content knowledge that pertain to vehicles and sports. The students will understand the following relationships: Work and energy, momentum and impulse, energy and momentum, and impulse to work.
District Standards:

This unit addresses the Standard for Physical science (grades 9-12), which is concerned with energy and momentum conservation (NSES, p. 180), and forming a testable hypothesis along with properly testing and analyzing the results (NSES p. 175). The specific areas are: