As you watch this video, think about the following questions:
- Are energy transformations or energy conversions efficient in everyday objects?
- How efficient is a car?
- How efficient are the energy conversions in the human body?
The law of conservation of energy states that energy cannot be created or destroyed, but only converted from one form to another. Some energy may be lost to friction and air resistance, but the overall amount of energy stays the same. Most energy conversions are not very efficient. There's always a loss of useful or usable energy. A perfect energy conversion is impossible because this means that all the energy in the conversion would be turned to useful work. For example, a car is about 22% efficient, as much of the energy changes to heat and is used to overcome friction and inertia. The human body uses food as its fuel source. The chemical energy is converted to energy to help us move, breathe, think, and carry on all the other important functions that keep us alive. However, the human body is not very efficient. And during this conversion 95% of this chemical energy is converted to heat. Think of the last time you were very active and produced a lot of heat as a result.
Remember, energy cannot be created or destroyed as it is converted from one form to another. Here is an example. Look at this set up of five metal balls hanging from strings of the same length. The balls are all exactly the same. What do you think will happen if we lift one ball and then release it? If you thought that only one ball from the end would pop out, you're correct. Notice that it goes up almost as high as the first ball and then swings back, hitting the group and sending the first ball flying again. Each time the height of the two balls reaches lower until eventually they would stop this movement. This back and forth movement doesn't continue forever because energy is being changed to heat due to friction and air resistance. Now let's change things a bit. This time we will release two balls from one side. What do you think will happen? Pause the program and make your prediction. As you can see, two balls from the other side bounce out. Scientists call this the law of conservation of energy, which simply means energy is neither created nor destroyed. It is transferred or changed from one form to another. Let's try another set up. This time we will release three balls from one side. There are only two balls left hanging straight down. What do you think will happen this time? Pause the program and make your prediction. Were you surprised by what happened? One of the balls joins the two so that the amount of kinetic energy is equal. Now let's change things by releasing one ball from each side at the same time. Pause the program and make your prediction. Did you expect the balls to bounce back out? As long as the strings don't get tangled, you could do this with different numbers of balls. When we lift a ball to a certain point before dropping it, we have given it potential energy. Someone has used his or her muscles against gravity to lift the ball to a certain height. When the ball is released, it begins to swing down. The potential, or stored energy, is changing to kinetic energy, or energy of motion. When the ball hits the group of balls, the energy is transferred, or moved, from one ball to the next until the ball on the end is pushed into the air against gravity. This ball reaches a certain height and stops. At that point, it has the potential energy. Then it begins to swing down, which means its potential energy is changing to kinetic energy. Look at this amusement park ride and think about how it might be another example of potential energy changing to kinetic energy, and then kinetic energy changing to potential energy, and so on and so on. How much kinetic energy an object has depends on two things: how much mass the object has and how fast the object is moving. Forms of energy are all around us.
Law of Conservation of Energy
How is energy transferred in the group of swinging pendulums?
Human Body
Is the human body efficient in converting energy?
