(STE) Toys and Forms of Energy Lesson
Toys and Forms of Energy
We all had a favorite toy as a child, but have you ever stopped to think what made it so special? Why did we love to play with it for hours on end? Chances are it would capture our imagination with movement or perform some action that we found irresistible. Many of the toys that we loved so much required some form of energy to carry out its action. Energy is the ability to do work. When our toys were moving, making sounds or producing light they were producing some form of work from the energy that was given to the toy. Whether it was a toy car that you would wind up and send racing across the floor or a video game that captured your attention for hours, most toys require energy to operate. In this lesson we are going to investigate how toys use different forms of energy and where this energy comes from.
Basic Forms of Energy
There are two basic forms of energy; potential and kinetic. Potential energy is stored energy that can be used to do work but is currently being stored for later use. Kinetic energy on the other hand is the energy of motion. If an object is performing work, it is taking advantage of kinetic energy. Potential energy and kinetic energy are related in that as one increases, the other decreases.
We can use a bouncing ball as an example. If I am holding the ball in the air, it has gravitational potential energy. I can hold it there for a long period of time and the ball is not doing work. Eventually if I let the ball go it will start to move towards the floor, increasing its speed as it falls. As the ball moves toward the floor, its kinetic energy increases and the amount of potential energy decreases. When it eventually hits the floor, it has no gravitational potential energy and all of its energy at that point is kinetic. Some of the kinetic energy is transferred to the floor and the rest of the energy is converted back to potential energy as the ball bounces and rises back into the air. This will happen over and over again until the ball finally transfers all of its energy to the floor. At this point, the ball has no gravitational potential energy or kinetic energy and will come to rest on the floor.
We can express this motion mathematically with the following equations:
Potential Energy (PE) = m x g x h
Kinetic Energy (KE) = 1/2 mv2
Total Energy = Kinetic Energy + Potential Energy
m = mass, g =gravity, h = height and v = velocity
*On Earth gravity = 9.8 m/s2 and is considered a constant
Example Problem:
(a) If an object has a mass of 2 kg and is sitting above the floor at a height of 1m, how much potential energy does it contain?
(b) What is the kinetic energy of the object as it sits on the shelf?
(c) What is the potential energy and kinetic energy if the object falls and reaches a point half way to the floor?
(d) What is the potential energy and kinetic energy the moment that the ball hits the floor?
Example Solution:
(a) PE= m x g x h
PE = (2kg)(9.8m/s2)(1m)
PE = 19.6 J
(b) If the object is sitting on the shelf it is not moving. The potential energy is equivalent to all of the gravitational potential energy that the object contains. In this case kinetic energy would be 0 J.
(c) If the object is at the half way point, half of the energy is still stored as potential energy and the other half has been converted to kinetic energy. From solution (a), 19.6 J ÷2 = 9.8 J PE = 9.8 J and KE = 9.8 J
(d) The instant the ball hits the floor all of its energy has been converted to kinetic energy so PE= O J and KE= 19.8 J.
Just as a bouncing ball utilized gravitational potential energy, many toys use other forms of potential energy. Toys use this potential energy to carry out their various functions by converting it to kinetic energy to create movement, sound and light that we all enjoy. We will discuss several types of potential energy utilized by toys and see how energy transformations occur as the toy operates.
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