# Homework Help: General Question

1. Apr 8, 2006

### cristovian

If a cricket ball and a plastic bullet traveled with the same amount of energy which would hurt more?

I figure that in order for there energy to be equal the velocity of the bullet would have to be greater than the velocity of the bullet. So the bullet would hit you at a higher velocity than the ball. Plus the pain from the ball acts over a greater area, whereas the pain of the bullet acts on a very small spot which i feel would hurt more.

I think the answer is, that the plastic bullet hurts more, but i need some help in explaining it.or if im wrong, let me know why im wrong so i can correct the question.

2. Apr 8, 2006

### Kurdt

Staff Emeritus
The more energy travelling through a smaller area would probably hurt more yet you have to consider other things such as the actual make up of the object. A cricket ball is solid and fairly inelastic so no energy will be absorbed by deforming its shape. I dare say a plastic bullet is designed to hurt but not kill and thus most energy will go into 'crumpling' the bullet.

3. Apr 9, 2006

### daniel_i_l

Why do you think that the plastic hurts more? If That is true it could be because of the fact that the real bullet cuts through the skin so fast that it hurts less?

4. Apr 9, 2006

### cristovian

what do you mean by "crumpling" the bullet.

Do you mean that since the cricket ball will probably bouce off further than the bullet would "bounce" off that more energy is transferred into that spot and will thus hurt more.

Last edited: Apr 9, 2006
5. Apr 9, 2006

### BobG

I'm not sure how hard a cricket ball is, but I think he means the shape of your skull would be more likely to be deformed than the shape of the cricket ball.

Asking which will "hurt more" is a pretty ambiguous question and involves more than physics. More energy is concentrated on a small area for the plastic bullet, but a lot of the energy is dissipated in the plastic bullet deforming its shape. The bullet might still 'sting' a lot more if there's still more energy per area, but more nerves would be sending alarm messages to your brain for a cricket ball - and they would probably be sending alarm messages for a longer period of time.

6. Apr 9, 2006

### brewnog

Correct me if I'm wrong, but I think pain is a pretty subjective concept and is pretty hard to quantify?

7. Apr 9, 2006

### Hootenanny

Staff Emeritus
Cricket balls are quite hard (I would say that they are harder than plastic bullets), therefore I would tend to say that a cricket ball would deform less than a plastic bullet. As they both posses equal amounts of energy I would say that more energy would be used in deforming you if a cricket ball hit you than if a plastic bullet hit you.