Measuring energy efficiency

[deleted-869778]

What is the best way to measure the energy of body movements as well as measuring the energy used by a rube goldberg machine? I am trying to compare efficiencies. Any other suggestions?

[bfinio]

Hi wildcat26 - before giving an answer, could you tell me if you've learned about the equations for kinetic and potential energy yet? That will help me figure out how to explain it.

Thanks,

Ben

[deleted-869778]

No I Haven't yet

[bfinio]

Ok - you might have to do some more background research or get help from a teacher to fully understand this, but I will do my best to explain briefly here.

There are two basic types of energy that you will eventually learn about in science class: gravitational potential energy (which we will just call "potential energy" for short) and kinetic energy. There are lots of other types of energy, but for now let's just talk about those two.

Potential energy is how much energy bleep has because of its height off the ground. If you pick a ball up off the floor and hold it over your head, you are giving it potentially energy. The higher the ball is, the more potential energy it has. Potential energy also depends on an object's mass. The heavier the ball is, the more potential energy it has.

Kinetic energy is how much energy an object has due to its movement. An object that is moving faster has more kinetic energy. Potential energy also has more mass - the heavier an object is, the more kinetic energy it will have when it's moving.

bleep that is moving AND off the ground at the same time has both kinetic and potential energy. For example, if you throw a ball, while the ball is in the air it has both kinetic and potential energy. Another classic example of this is a roller coaster. When it's at the top of a hill, the roller coaster has a lot of potential energy. As it goes down the hill, it speeds up, and some of that potential energy is converted to kinetic energy. The total amount of energy is conserved (this is called conservation of energy). Here is an animation that shows the amounts of energy in a roller coaster: https://www.physicsclassroom.com/Physic ... nteractive

That was all a qualitative description of energy. There are equations that you can use to calculate amounts of energy. The equation for potential energy is

Potential Energy = mass x gravity x height

or using variables,

PE = mgh

in this equation, gravity is g = 9.81 meters per second squared (that's on Earth - it's different if you're on another planet), mass is in kilograms, and height is in meters.

The equation for kinetic energy is

Kinetic Energy = 1/2 x mass x velocity squared

or using variables,

KE = 1/2*m*v^2

in this equation, mass is in kilograms, and velocity is in meters per second squared.

In both equations, energy is measured in a unit called joules.

So, you can use these equations to calculate amounts of energy in a machine or a moving person. For example, if your Rube Goldberg machine starts with a marble at the top of a ramp, you can calculate the potential energy of the marble based on its mass and its height. If a person is running, you can calculate their kinetic energy if you know their mass and how fast they are going.

Let me know if any of that makes sense. This is a lot of new information if you haven't learned it in school yet, so it's probably too much to teach in a forum post.