What happens to the lost energy in these situations?

In summary, when energy is lost due to friction, braking, or air resistance, it is converted into heat energy. This process is always inefficient and results in a decrease in the overall amount of energy. However, energy is conserved and can be converted from one form to another.
  • #1
Kaxa2000
71
0
What happens to the "lost" energy in these situations?

(a) A box sliding across the floor stops due to friction. How did friction take away that KE and what happened to that energy?

(b) A car stops when you apply the brakes. What happened to its kinetic energy?

(c) air resistance uses up some of the gravitational potential energy of a falling object. What type of energy did the lost PE become?

(d) When a returning space shuttle touches down on the runway, it has lost almost all its KE and gravitational PE. Where did all that energy go?

==========================

(a) I know the energy goes into the Earth but I'm not sure how friction takes away the KE

(b) The KE goes into the Earth ?

(c) does some of the PE get transferred as KE to the surrounding air?

(d) The earth?

correct me if I'm wrong
 
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  • #2


Well, in many of your examples the energy is translated into heat(thermal energy).

The energy doesn't "go" anywhere or into anything. It is energy, not matter.

Let us talk about the car question though.(b)
When you apply the breaks, friction is created. This friction generates heat.
Now, what if you stopped your car by driving up a hill until the car stopped?
The energy would have changed from kinetic energy to potential energy.

The basic lesson is that energy can be changed from one state to another.
The secondary lesson is that this process is always inefficient, and you will always have less energy when it is over.

Hope that helps!
 
  • #3


Kaxa2000 said:
(a) A box sliding across the floor stops due to friction. How did friction take away that KE and what happened to that energy?

(b) A car stops when you apply the brakes. What happened to its kinetic energy?

(c) air resistance uses up some of the gravitational potential energy of a falling object. What type of energy did the lost PE become?

(d) When a returning space shuttle touches down on the runway, it has lost almost all its KE and gravitational PE. Where did all that energy go?

==========================

(a) I know the energy goes into the Earth but I'm not sure how friction takes away the KE

(b) The KE goes into the Earth ?

(c) does some of the PE get transferred as KE to the surrounding air?

(d) The earth?

correct me if I'm wrong

In all of these situations, if you were to take very careful temperature measurements of

(a) the box and the ground,

(b) the brake rotor and brake pads,

(c) the air through which the object fell and the object,

(d) the space shuttle and the air along its path,

you would find a rise in temperature. In each case kinetic energy has been turned into the type of molecular motion that gives rise to what we call heat.
 
  • #4


PuckSR said:
The secondary lesson is that this process is always inefficient, and you will always have less energy when it is over.

This is just plain wrong. Energy is conserved. In many situations, in order to see that, you have to consider all possible forms into which it might have been changed. That is the point of doing this type of problem.
 
  • #5


Yea that does help...thanks...but what about question c? Was I right about that? When an object falls some of the PE gets translated into KE which slows the object down right?
 
  • #6


Kaxa2000 said:
Yea that does help...thanks...but what about question c? Was I right about that? When an object falls some of the PE gets translated into KE which slows the object down right?

Nope. The translation of PE into KE speeds the object up to maintain the conservation of energy. Some of the PE is lost to heat, so the correct equation is

PE goes to KE + energy dissipated as heat
 
  • #7


Oh okay thanks
 
  • #8


This is just plain wrong. Energy is conserved. In many situations, in order to see that, you have to consider all possible forms into which it might have been changed. That is the point of doing this type of problem.

Absolutely correct...I don't really know what I was trying to say there...
If you account for all energy, it should be a perfectly balanced equation
 

Related to What happens to the lost energy in these situations?

1. What is lost energy?

The term "lost energy" refers to energy that is not able to be converted into a usable form or transferred to another system. This can occur due to inefficiencies or limitations in a system.

2. Where does lost energy go?

Lost energy does not go anywhere, it simply remains in its current form and cannot be utilized. For example, in a car engine, lost energy may be in the form of heat, sound, and friction, but it does not go to another location or disappear.

3. Can lost energy be recovered?

In many cases, lost energy cannot be fully recovered. However, there are some technologies and methods that aim to recover and reuse lost energy, such as regenerative braking in vehicles.

4. How does lost energy affect the efficiency of a system?

Lost energy can significantly decrease the efficiency of a system, as it means that not all of the input energy is being converted into the desired output. This can result in wasted resources and higher costs.

5. What are some examples of situations where energy is lost?

Energy can be lost in various situations, such as in the form of heat in a light bulb, sound in a speaker, or friction in a machine. It can also be lost during energy transfer, such as in power lines or during energy storage processes.

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