I need to know amount of force apploed to an object

[barett468]

Can someone please answer the question below for me.

Weight of object is 220 lbs.

Speed object is 40 mph.

What is he fore in psi?

 

[Deleted member 4993]

Can someone please answer the question below for me.

Weight of object is 220 lbs.

Speed object is 40 mph.

What is he fore in psi?

As posted, the problem cannot be answered.

Please post the exact problem presented to you.

 

[Dr.Peterson]

Can someone please answer the question below for me.

Weight of object is 220 lbs.

Speed of object is 40 mph.

What is the force in psi?

Force is not measured in psi; that is a pressure. Therefore, I assume this is not a problem from a physics class, where it would have been asked correctly, but a real-life question. Are you asking, as many people who don't know physics do, about the force when a falling or thrown object hits something?

If we could find the force in pounds, we could find the pressure by dividing that by the area (in square inches) over which the force is applied, to get a pressure in pounds per square inch. (That would be the average pressure, and there might be more pressure at some points than others.) For example, a ball hits you with less pressure than an arrow (assuming the same forces), which is why the arrow goes in farther.

But the force depends on something else that we don't know: the distance over which the object is stopped. This, in turn, depends on many variables, such as the material of which both objects are made, their shape, and so on. For example, impact tests on cars show great variation due to the construction of the cars, and how they hit. The longer the crumple zone (longer time to stop), the less force. In the same way, your face hitting an air bag vs. a windshield experience very different forces, pressures, and deformations, because the air bag takes longer to stop you.

 

[barett468]

Force is not measured in psi; that is a pressure. Therefore, I assume this is not a problem from a physics class, which would have been asked correctly, but a real-life question. Are you asking, as many people who don't know physics do, about the force when a falling or thrown object hits something?

If we could find the force in pounds, we could find the pressure by dividing that by the area (in square inches) over which the force is applied, to get a pressure in pounds per square inch. (That would be the average pressure, and there might be more pressure at some points than others.) For example, a ball hits you with less pressure than an arrow (assuming the same forces), which is why the arrow goes in farther.

But the force depends on something else that we don't know: the distance over which the object is stopped. This, in turn, depends on many variables, such as the material of which both objects are made, their shape, and so on. For example, impact tests on cars show great variation due to the construction of the cars, and how they hit. The longer the crumple zone (longer time to stop), the less force. In the same way, your face hitting an air bag vs. a windshield experience very different forces, pressures, and deformations, because the air bag takes longer to stop you.

Thanks very much for your reply.



I need to know how much force will be applied in psi to an axle on a 220 lb motorcycle when it hits a bump (or runs into a wall) at 40 mph so I can determine if the axle material I want to use has enough ultimate shear resistance, which in this case is 53,000 psi. Since the motorcycle has suspension, the actual force applied to the axle will be less than what it would be if it had no suspension, therefore, my 40 mph speed is actually on the high side and I'm just using it as a speed that is higher than the axle will see so I know I have a safety margin. If the force on the axle at an impact speed of 40 mph is less than the 53,000 psi shear rating of the material I plan to use, the material will be more than strong enough and my axles won't break when I ride it. The motorcycle is being used for vintage motocross/dirt bike racing.

 

[barett468]

Force is not measured in psi; that is a pressure. Therefore, I assume this is not a problem from a physics class, which would have been asked correctly, but a real-life question. Are you asking, as many people who don't know physics do, about the force when a falling or thrown object hits something?

If we could find the force in pounds, we could find the pressure by dividing that by the area (in square inches) over which the force is applied, to get a pressure in pounds per square inch. (That would be the average pressure, and there might be more pressure at some points than others.) For example, a ball hits you with less pressure than an arrow (assuming the same forces), which is why the arrow goes in farther.

But the force depends on something else that we don't know: the distance over which the object is stopped. This, in turn, depends on many variables, such as the material of which both objects are made, their shape, and so on. For example, impact tests on cars show great variation due to the construction of the cars, and how they hit. The longer the crumple zone (longer time to stop), the less force. In the same way, your face hitting an air bag vs. a windshield experience very different forces, pressures, and deformations, because the air bag takes longer to stop you.

I may have found something that might help.


Can a figure be calculated in psi for the load on the axle with a suspension speed of 600" per second?

In other words, how much initial force (or pressure etc) will be exerted on an axle of a 220 lb motorcycle when it hits a bump hard enough to collapse the suspension at a rate of 600 inches per second? Obviously the force/pressure decreases the further the suspension collapses so the amount of force/pressure decreases as well.

 

[sinx]

Thanks very much for your reply.



I need to know how much force will be applied in psi to an axle on a 220 lb motorcycle when it hits a bump (or runs into a wall) at 40 mph so I can determine if the axle material I want to use has enough ultimate shear resistance, which in this case is 53,000 psi. Since the motorcycle has suspension, the actual force applied to the axle will be less than what it would be if it had no suspension, therefore, my 40 mph speed is actually on the high side and I'm just using it as a speed that is higher than the axle will see so I know I have a safety margin. If the force on the axle at an impact speed of 40 mph is less than the 53,000 psi shear rating of the material I plan to use, the material will be more than strong enough and my axles won't break when I ride it. The motorcycle is being used for vintage motocross/dirt bike racing.

this is a mechanics of materials problem.
the maximum stess will be in bending (not shear),
where bending stress=Mc/I. (in lbs/in² or N/m² or whatever)
and is about the neutral axis;
if the axle is round, the neutral axis is at its geometric center.
you then calculate the "area moment of inertia"=I,
for circular shape, I=1/4pi_*r⁴ ​
c is the distance from the neutral axis (radius of the axle in this case)
M=F x d , and d (distance) would be the radius of the wheel (as if the edge of the wheel was hit from the side, i.e you landed with all the wieght on the outside edge of the wheel, sideways)

the force you caclulate from F=ma, or Fdt=mdv, impulse momentum, so you need the time, or a reasonable estimate. (you know V₂, V₁=0).

you can calculate shear when you have the force and area, Stress (in shear)= F/A
A (area)= the x-sect area of the shaft.
added to bending gives the total, but you will find that shear stress is small in comparison to bending.

you also want to compare your max psi load to the tensile strength of the material, not the ultimate strength.