# Efficiency! What makes it less than 100%?

1. ### iRamie

19
1. The problem statement, all variables and given/known data
List a couple factors that make efficiency less than 100%.

2. Relevant equations
Efficiency = Eout / Ein
Eout = mgh
Ein = Work = FD

3. The attempt at a solution

IDK :\

2. Science news on Phys.org
3. ### thegreenlaser

520
A better way to look at efficiency is (useful output energy)/(input energy). A tank of gasoline has a certain amount of stored energy, however your car's motor produces a lot more than forward motion. All of that energy in the gasoline goes somewhere, but only a certain part goes to moving your car forward. For example, your engine gets very hot as it runs: Where does the energy for this heat come from? If all you want is forward motion, how is the production of this heat going to affect the amount of useful energy you get out of a tank of gasoline? (in this case useful energy is used for forward motion of the car)

Essentially, I understand the question to be: what sort of things 'waste' energy in a system? What sort of things decrease the amount of useful energy you get?

4. ### iRamie

19
No like i mean, in a situation where there is an inclined plane (RAMP). And you are pushing an object up there.
In that situation what makes it less than 100%

5. ### AlexChandler

283
With this definition of efficiency it will be less than 1 if the object starts at some speed V0 and ends at some speed V1 with V0<V1.

This is because

$$W = \Delta K.E. + \Delta G.P.E.$$

if the change in kinetic energy is positive, then

$$W > mgh$$

and

$$\frac{mgh}{W} < 1$$

But i'm not sure that this definition for efficiency really makes sense.

6. ### iRamie

19
Im in grade 11 btw so its introductory mechanics lol

We have a lab in which there is a ramp with one end on the floor and the other end is on top of a few textbooks. Therefore, it has a slope, and an object is lifted using the ramp and the force is measured using a newton scale.
So in this case, what makes it less than 100%.
Assume the object is moving at constant velocity.

7. ### AlexChandler

283
Or you can take the advice of thegreenlaser, and say that friction will cause efficiency to be less than 100%. Friction is a much simpler and better answer in my opinion.

8. ### iRamie

19
Okay so can i say Friction will cause more applied force as a result it causes less efficiency.
Is there anything else? Because it asks for 2 Major Factors.

9. ### AlexChandler

283
Perhaps air resistance. What do you think?

520