Question about the transfer of kinetic energy.

[Humberto]

Suppose you have two balls. One is a tennis ball and the other is a bouncy ball of equal weight and size, the type made of soft rubber which bounces very high when you drop it.

Which of the two is more likely to break a window if thrown at the same speed?

Please critique the following possible arguments:

1. The bouncy ball transfers less energy to the window because more of its kinetic energy is retained when the ball bounces back than with the tennis ball. Hence the bouncy ball is less likely to break the window.
2. For every action there is an equal but opposite reaction. The fact that the bouncy ball bounces back further than the tennis ball means the window had to exert a greater force on the bouncy ball during impact than with the tennis ball. Hence the bouncy ball had to exert the same force on the window, greater than the force that the tennis ball exerted during impact. Hence the bouncy ball is more likely to break the window.
3. The balls are equally likely to break the window, being the same weight and size.

 

[Geriatrix]

Depends on the window, and the speed, the distance, air density and a whole host of factors.

But, mostly, the general effect should be similar.

 

[Elimentals]

The rubber ball broke the window, so don't know how you want to interpret it.

PS: you ow me a new window.

 

[Scooby_Doo]

I would say the bouncy ball would break it as it has a smaller surface area when it hits the window. The larger tennis ball would displace its force over a larger area and hence there is more chance of the window withstanding the force.

edit

example 10 kg of force on a 1cm squared area vs 10kg of force on a 1meter squared area.

 

[Mike Hoxbig]

#3. You're measuring the force exerted at the point of impact. What happens thereafter is irrelevant.

 

[Unhappy438]

#3 , Force = Mass.Acceleration therefore Equal Mass , Equal Acceleration means equal Force.

 

[Archer]

#3 , Force = Mass.Acceleration therefore Equal Mass , Equal Acceleration means equal Force.

But they apply the force over a different area. Even though they are the same size, they will deform differently. So its not 3

edit: the bouncy ball undergoes greater acceleration, therefore applies the greater force. Not sure how that ties into my first point yet But definately means they are not equally likely to break the window

edit2: I'm confused again, let me break out the math...

 

[Humberto]

Suppose the velocity of both balls before impact is v. As they bounce back, their velocities are, for the sake of argument, -5/6v for the bouncy ball and -1/3v for the tennis ball. Hence the change in magnitude of velocity is 11/6v for the bouncy ball but only 4/3v for the tennis ball. The impact with the window has caused a greater change in velocity with the bouncy ball than with the tennis ball.

 

[Mike Hoxbig]

But they apply the force over a different area. Even though they are the same size, they will deform differently. So its not 3

It's not significantly different. If we're going to factor in these additional variables, then we'll need more information about the window itself - specifically it's maximum load-bearing capacity per unit area

 

[droplet]

the bouncy ball changes direction in a shorter space of time, transferring its energy to the window more quickly. greater shock to the window - it will struggle to dissipate the energy more in the case of the bouncy ball. bouncy ball more likely to break window.

 

[Archer]

It's not significantly different. If we're going to factor in these additional variables, then we'll need more information about the window itself - specifically it's maximum load-bearing capacity per unit area

Tennis balls have a pretty high coefficient of restitution, so before the OP gave us the hugely spaced numbers, I think it was relevant. The glass load bearing capacity is actually completely irrelevant, since its the same whether you use a tennis ball or bouncy ball, its a common variable. Actually any properties of the window are irrelevant, since its all common

edit: sticking with this, should be correct

the bouncy ball undergoes greater acceleration, therefore applies the greater force. (therefore most likely to break the window)

 

[Park@82]

The rubber ball broke the window, so don't know how you want to interpret it.

PS: you ow me a new window.

bwahahahah

 

[SaiyanZ]

If the speed and weight is the same then the force is the same if applied to the same surface area. So the ball that deforms more and thus spreads the force over a greater surface area will have a lower chance of breaking the window.

 

[Mike Hoxbig]

Tennis balls have a pretty high coefficient of restitution, so before the OP gave us the hugely spaced numbers, I think it was relevant. The glass load bearing capacity is actually completely irrelevant, since its the same whether you use a tennis ball or bouncy ball, its a common variable. Actually any properties of the window are irrelevant, since its all common

Ok, let's ignore any external variables for now. Do you agree that the ball (any ball) will only bounce if there is a force exerted on it by the window (Newton's first law)? Now two balls of the same size, same mass and travelling at the same speed will each exert the same amount of force on the window as the window exerts on them.

I understand the point you're trying to make, but from the OP there is insufficient information to deduce the breaking points of the window, or the chemical composition of the rubbery ball.

 

[Unhappy438]

If the speed and weight is the same then the force is the same if applied to the same surface area. So the ball that deforms more and thus spreads the force over a greater surface area will have a lower chance of breaking the window.

Tennis balls have a pretty high coefficient of restitution, so before the OP gave us the hugely spaced numbers, I think it was relevant. The glass load bearing capacity is actually completely irrelevant, since its the same whether you use a tennis ball or bouncy ball, its a common variable. Actually any properties of the window are irrelevant, since its all common

edit: sticking with this, should be correct

None of these answers are part of the question. We can only choose between 1,2,3 and i see 3 as the most correct in this case.

 

[droplet]

what i said earlier. that. yes, it's right.

 

[Archer]

Ok, let's ignore any external variables for now. Do you agree that the ball (any ball) will only bounce if there is a force exerted on it by the window (Newton's first law)? Now two balls of the same size, same mass and travelling at the same speed will each exert the same amount of force on the window as the window exerts on them.

But they leave at different velocities... so how could they have undergone the same acceleration?

I understand the point you're trying to make, but from the OP there is insufficient information to deduce the breaking points of the window, or the chemical composition of the rubbery ball.

We actually do have enough info, OP has given us what we need to figure out the coefficient of restitution. Bouncy ball in this case has a much higher coeff. Therefore, bouncy ball is more likely to break the glass. And again, breaking point of the window is completely irrelevant, its a common variable.

what i said earlier. that. yes, it's right.

/highfive for getting it right

 

[Unhappy438]

But they leave at different velocities... so how could they have undergone the same acceleration?

OP says they leave at the same speed...

 

[SaiyanZ]

OP says they leave at the same speed...

Nope.

 

[Unhappy438]

Nope.

Suppose you have two balls. One is a tennis ball and the other is a bouncy ball of equal weight and size, the type made of soft rubber which bounces very high when you drop it.

Which of the two is more likely to break a window if thrown at the same speed?

Please critique the following possible arguments:

1. The bouncy ball transfers less energy to the window because more of its kinetic energy is retained when the ball bounces back than with the tennis ball. Hence the bouncy ball is less likely to break the window.
2. For every action there is an equal but opposite reaction. The fact that the bouncy ball bounces back further than the tennis ball means the window had to exert a greater force on the bouncy ball during impact than with the tennis ball. Hence the bouncy ball had to exert the same force on the window, greater than the force that the tennis ball exerted during impact. Hence the bouncy ball is more likely to break the window.
3. The balls are equally likely to break the window, being the same weight and size.

?