Collisions/conservation of energy[conceptual]

  • Thread starter anti404
  • Start date
In summary, this is a problem with the way we explained elastic collisions to our class. The calculations that we did were not completely accurate, and the loss of energy following the collision may have been larger than we thought.
  • #1
anti404
20
0
as alluded to in the title, this isn't so much a "problem" as a concept for a lab/experiment we performed.
so, for some reason I was sure that a collision between two hockey pucks of roughly equal masses would result in an elastic collision, but I calculated the KE, and the two values were different, meaning it wasn't elastic. is this, uh, okay? from the way our professor explained the concept of elastic collisions[though not necessarily the lab itself], this type of collision[two similar masses moving at angles and producing a glancing collision] should result in conserved KE. but, maybe I just didn't understand what he was trying to say.
 
Physics news on Phys.org
  • #2
In the real world, there is no such thing as a perfectly elastic collision, and therefore, some kinetic energy will always be lost. But the loss of energy between a collision of 2 pucks should not be as huge, say, as the loss would be in the case of 2 marshmallows colliding . How much did you lose? Did you do the calculations correctly?
 
  • #3
the calculated KE before the collision was around 8.58*10^-3J. KE after was about 5.97*10^3J. so it lost, approximately. 2.5*10^-3J of energy following the collision.

I may have done the calculations incorrectly, but the more plausible situation is that my derived equations may be incorrect; I'm asking on here to see if these answers would be somewhat plausible, or if I should try to completely change everything.
 
  • #4
Elastic collision processes are taught in a complicated way by most teachers. There is an utterly simple method - it is geometrical, however. But once we appreciate the result, we can do the algebra and get the required numbers.

First, forget about real life situations, because they are most complicated - in fact, that is the reason great scientists have resorted to thought experiments (ideal world situations).

1D collisions (head-on) are the simplest to understand. Solve the problem in center of mass reference frame, first. (just as you do a multiplication or division problem using logarithms). Then , in the next step you can transform the result to the frame of your interest. (just as you do a multiplication or division result using antilogarithms).
 

1. What is the law of conservation of energy?

The law of conservation of energy states that energy cannot be created or destroyed, but can only be transformed from one form to another. This means that the total amount of energy in a closed system remains constant.

2. How does conservation of energy apply to collisions?

In a collision, the total amount of kinetic energy before the collision is equal to the total amount of kinetic energy after the collision. This is because energy is conserved and cannot be lost during the collision.

3. What is an elastic collision?

An elastic collision is a collision in which there is no loss of kinetic energy. This means that the total kinetic energy before the collision is equal to the total kinetic energy after the collision.

4. What is an inelastic collision?

An inelastic collision is a collision in which there is a loss of kinetic energy. This means that the total kinetic energy before the collision is greater than the total kinetic energy after the collision.

5. How does the conservation of energy apply to real-life collisions?

In real-life collisions, there is always some energy lost due to factors such as friction and sound. However, the law of conservation of energy still applies and the total amount of energy in the system remains constant, it is just transformed into different forms of energy.

Similar threads

  • Introductory Physics Homework Help
Replies
4
Views
992
  • Introductory Physics Homework Help
Replies
2
Views
2K
  • Introductory Physics Homework Help
Replies
6
Views
2K
  • Introductory Physics Homework Help
Replies
4
Views
3K
  • Introductory Physics Homework Help
2
Replies
55
Views
1K
  • Introductory Physics Homework Help
Replies
10
Views
948
  • Introductory Physics Homework Help
Replies
2
Views
2K
  • Introductory Physics Homework Help
2
Replies
35
Views
4K
  • Introductory Physics Homework Help
Replies
4
Views
1K
  • Introductory Physics Homework Help
Replies
6
Views
810
Back
Top