How Does Weight Change When an Object Falls?

In summary, a 1kg weight dropped from the same 5m shelf will feel five times as much force as a 1lb weight dropped from the first question.
  • #1
Theatre_Kid
2
0
Mostly for self interest:
If I drop a 1lb weight from 15 ft (5m), what does it weigh when it hits the floor.
If I have a 10lb weight and it drops from the same 5m shelf, does it weigh 10 times as much as my 1 lb weight from the 1st question?

I may have the wrong terminology, but basically the 1lb weight in my hand weighs 1lb. If I through it in the air and catch it, it is heavier when it hits my hand, because of the force of gravity pulling it back down. If that fall is 5 meters, what is the weight the floor will feel when the object hits the ground.
 
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  • #2
Hi Theatre_Kid. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif

Without knowing the muscle strength you can adeptly repeatedly exert, I don't think it is possible to make a comparison the way you are asking.

A comparison that could be made is: if a 1lb weight when gently sat on a spring depressed it by x inches, how many inches would the spring depress if that weight were dropped on it from 15 ft.
 
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  • #3
I may have the wrong terminology, but basically the 1lb weight in my hand weighs 1lb. If I through it in the air and catch it, it is heavier when it hits my hand, because of the force of gravity pulling it back down. If that fall is 5 meters, what is the weight the floor will feel when the object hits the ground.

When the 1lb weight hits the floor it will be traveling at some velocity V. You can work that out using...

V = Sqrt(2as)

where
a is the acceleration due to gravity (9.81m/s2)
s is the displacement or height it fell from (eg 5m)

The problem is working out the force with which the weight hits the ground. Suppose the ground was soft and the weight sank in (s) 5cm (0.05m) before coming to rest. You could run the equation in reverse to work out the average deceleration (d)...

d = V2/2s

Then you could use Newtons laws to estimate the force (F) ...

F = md

where
m=mass of the object.

Note that the harder the ground the shorter the stopping distance. If the 1lb weigh somehow hit the ground and stopped dead the deceleration would be very large, potentially infinite. Therefore the force on the object/ground would also be very large. That's why things dropped onto concrete tend to break.

(Aside: The above makes some assumptions that aren't always valid but that's another story).
 
  • #4
Thank you, both for the welcome and the answer.
Is there a way to know the stopping distance? I get that concrete would be shorter than wood or foam, but is there a property (density? hardness) of a given material that would let me know how to calculate that, or something I just make an assumption for and move on?

Also, am I right in believing that weight (pounds) is a measure of force? IE it measures the force of gravity on a given object?

Finally, does it matter if I'm mixing imperial and metric units (a 1lb weight falling 5 meters)
 
  • #5


I would like to clarify that weight is a measure of the force of gravity acting on an object and is typically measured in units of mass (such as pounds or kilograms). The weight of an object can vary depending on the strength of the gravitational force, such as on different planets or at different elevations on Earth.

In the scenario described, the 1lb weight in your hand will still weigh 1lb when it falls 15 ft (5m) and hits the ground. This is because the weight of an object remains constant regardless of its motion. However, when the weight hits the ground, it will experience a force equal to its weight multiplied by the acceleration due to gravity (9.8 m/s^2 on Earth). This force is what causes the weight to feel heavier when it hits your hand.

In the second scenario, the 10lb weight will also experience the same acceleration due to gravity when it falls from the same height and hits the ground. However, its weight will be 10 times greater than the 1lb weight due to its larger mass. Therefore, the force felt by the ground when the 10lb weight hits will be 10 times greater than the force felt by the ground when the 1lb weight hits.

I hope this explanation helps to clarify the concept of weight and its relationship to falling objects. It is important to remember that weight and mass are not the same and can often be confused. As a scientist, it is crucial to use precise terminology to accurately describe and understand scientific phenomena.
 

Related to How Does Weight Change When an Object Falls?

What is relative weight when falling?

Relative weight when falling refers to the weight of an object or person as they are in motion, typically during free fall. It takes into account the effects of gravity and acceleration on an object's weight.

How is relative weight when falling calculated?

The calculation for relative weight when falling involves multiplying the object's mass by the acceleration due to gravity. This can be expressed as W = mg, where W is the relative weight, m is the mass, and g is the acceleration due to gravity (9.8 m/s² on Earth).

Does relative weight change during free fall?

Yes, relative weight changes during free fall as the object is accelerating. As the object falls, its relative weight decreases due to the increase in speed and decrease in the effects of gravity.

How does air resistance affect relative weight when falling?

Air resistance, also known as drag, can affect the relative weight of an object during free fall. As an object falls, it experiences air resistance which can decrease its acceleration and therefore decrease its relative weight.

Can relative weight be negative when falling?

Yes, relative weight can be negative when falling. This occurs when the object is in a state of free fall and the force of gravity is greater than the object's weight. This can happen when the object reaches terminal velocity or when it is in a state of weightlessness, such as in orbit.

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