Falling down handphone. Why is it broken falling from high story building even though the force is the same.
A student ask me today, about the effect of distance to the force of an object falling down. In this case it's a about a hand phone, falling down. The question is wouldn't the force be the same, if it's 1 story vs 10 story building? But why if it's higher it will break?
I search for force vs momentum and I found out this web page. Nice explanation by 3 physics instructor of some sorts.How is force related to momentum?
or the link http://www.physlink.com/Education/AskExperts/ae462.cfm
The answer for my student question is that when the handphoen meet the floor at a very short time, the force will be very high due to the short time that the handphoen stopped. If it's a soft surface the handphone will have more time, so the force will be much lower.
Here is the most related answer.
Newton's 2nd Law tells us that force = mass x acceleration ( F = ma ).
Since acceleration is just how velocity changes over time, we can write
this as
F = m * v/t
Multiply both sides by time to arrive at
F t = m v
Since mv is momentum, we can see that the momentum conferred to an
object by a force equals the force times the time the force is applied.
Thus if a 15 Newton force to the right is applied to an initially
stationary object for 3 seconds, it will have a momentum of 45 kg m/s
to the right.
Most students who ask this question are usually trying to
figure out the reverse situation, however. If an object hits me with a
certain amount of momentum, how much force does it hit me with? Note
that due to Newton's 3rd Law, this can be calculated the same way. If a
thrown egg hits your hand with a momentum of 5 kg m/s, the force it
applies to your hand depends on the time it takes for your hand to
absorb the momentum. If you hold your hand very stiffly (and try to
make the egg stop in a very short period of time) the ball exerts a
high force on your hand, e.g. 100 N for 1/20th of a second. However as
anyone who has ever played in an egg toss knows, if you let your hand
'give' and extend the amount of time it takes to absorb the momentum,
the egg exerts a smaller force on your hand, e.g. 10 N for 1/2 a
second.
Answered by:
Rob Landolfi, Science Teacher, Washington, DC
I search for force vs momentum and I found out this web page. Nice explanation by 3 physics instructor of some sorts.How is force related to momentum?
or the link http://www.physlink.com/Education/AskExperts/ae462.cfm
The answer for my student question is that when the handphoen meet the floor at a very short time, the force will be very high due to the short time that the handphoen stopped. If it's a soft surface the handphone will have more time, so the force will be much lower.
Here is the most related answer.
Newton's 2nd Law tells us that force = mass x acceleration ( F = ma ).
Since acceleration is just how velocity changes over time, we can write
this as
F = m * v/t
Multiply both sides by time to arrive at
F t = m v
Since mv is momentum, we can see that the momentum conferred to an
object by a force equals the force times the time the force is applied.
Thus if a 15 Newton force to the right is applied to an initially
stationary object for 3 seconds, it will have a momentum of 45 kg m/s
to the right.
Most students who ask this question are usually trying to
figure out the reverse situation, however. If an object hits me with a
certain amount of momentum, how much force does it hit me with? Note
that due to Newton's 3rd Law, this can be calculated the same way. If a
thrown egg hits your hand with a momentum of 5 kg m/s, the force it
applies to your hand depends on the time it takes for your hand to
absorb the momentum. If you hold your hand very stiffly (and try to
make the egg stop in a very short period of time) the ball exerts a
high force on your hand, e.g. 100 N for 1/20th of a second. However as
anyone who has ever played in an egg toss knows, if you let your hand
'give' and extend the amount of time it takes to absorb the momentum,
the egg exerts a smaller force on your hand, e.g. 10 N for 1/2 a
second.
Answered by:
Rob Landolfi, Science Teacher, Washington, DC
posted by Zulkef Abdul at 4:02 PM
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