How to Calculate force exerted on a falling body?

In summary, the conversation involves an individual seeking to solve the problem of calculating the impact time of a falling object. They consider the force of the object's weight, but after studying various resources and considering the material and structure of the object, they realize they also need to consider the momentum and weight of the object. However, the calculation of impact time is complicated and depends on factors such as the elasticity and shape of the object and the surface it impacts with. The individual seeks to use experimental data and an accelerometer to estimate the impact time and the forces involved in the impact.
  • #1
Chandrasekar
13
1
TL;DR Summary
want to calculate force exerted on a body for that i need to calculate time duration on impact.
I'm curious about impact on falling object, so i have taken initiative to solve this problem.
I considered only force on the falling object would be its weight and taken F=mg. With only limited data m=.25kg and drop height h=1m.
Pondering on this consideration practically, it will have more force than its actual weight.
After Studying on various resources:
1. Link1
2. Link2
3. Link3
4. Link4
5. Link5
6. Link6*
7. Link7*
From this studies i have taken that i need to consider Momentum of the falling body and weight of the body. But in all the solution IMPACT TIME is assumed.
how do i calculate this impact time?
 
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  • #2
Welcome to PF.

You assume a drop height of 1 metre.
What does it then impact ?
How much time does it take to stop ?
 
  • #3
concrete - rigid base.
How much time does it take to stop ? This is what i want
I can calculate falling time.
i can't calculate the impact time and time taken to stop the object from initial velocity of the impact and 0 final velocity.
 
  • #4
Chandrasekar said:
How much time does it take to stop ?
It depends on what your object is made of and what the floor is made of, and their shapes. This is because the answer depends on how easy it is to deform the object. If you idealise both object and floor as perfectly rigid then the answer is zero time. If, on the other hand, you think of a water droplet then it's just going to splash, and the answer will be on the order of the time it takes the top of the droplet to hit the floor after the bottom touched (over-simplification warning!).

It's a difficult question - there is no single simple formula.
 
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  • #5
Chandrasekar said:
i can't calculate the impact time and time taken to stop the object from initial velocity of the impact and 0 final velocity.
This is what you need to do: either by your own experiments or researching the topic online. The impact time will also depend on the object. E.g. the force (per unit mass) of impact for a soft object will be less than for a hard object.
 
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  • #6
i can understand that it depends upon objects elasticity (material property), structure of the body and some energy will loss as heat, then how to calculate it?. what formula do i have to use in order to find it.

The final result, when i drop an object from a height i want to know what will happen to the object, will it break, or damage, solid.

for example when i drop a bottle i want to calculate how much damage it get.

At the beginning it seems very simple problem, as time stretches on study it become complicated to solve :(
 
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  • #7
Chandrasekar said:
i can understand that it depends upon objects elasticity (material property) and structure of the body, then how to calculate it?. what formula do i have to use in order to find it.
You need data on the properties of the materials involved.
Chandrasekar said:
The final result, when i drop an object from a height i want to know what will happen to the object, will it break, or damage, solid.
You need experimental data. There isn't just a single formula. Think about the car crash testing that gets done.
 
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  • #9
Thank you for all who responded to my request, i didn't expected this much response for my query.
but still, even its complicated i want to how to solve it.
 
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  • #10
Chandrasekar said:
Thank you for all who responded to my request, i didn't expected this much response for my query.
but still, even its complicated i want to how to solve it.
Using an accelerometer would be the most precise test to perform.

You can at least estimate a reasonable maximum distance the floor and body will deform during impact.

Copied from
https://en.wikipedia.org/wiki/G-force

”After a free fall from a height
h
followed by deceleration over a distance
d
during an impact, the shock on an object is
{\displaystyle (h/d)}
· ɡ0. For example, a stiff and compact object dropped from 1 m that impacts over a distance of 1 mm is subjected to a 1000 ɡ0 deceleration.”
 
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  • #11
Chandrasekar said:
At the beginning it seems very simple problem, as time stretches on study it become complicated to solve
True statement. Even for people who do this every day.

There is some good discussion of this in this thread: https://www.physicsforums.com/threads/greater-momentum-on-impact-means-greater-force.1049141/. While that thread is about cars smashing into walls, the principles are the same: a rigid impact has higher forces than a soft impact. And it is not always possible to calculate the hardness of the impact, and the resulting forces.
 
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  • #12
jrmichler said:
True statement. Even for people who do this every day.

There is some good discussion of this in this thread: https://www.physicsforums.com/threads/greater-momentum-on-impact-means-greater-force.1049141/. While that thread is about cars smashing into walls, the principles are the same: a rigid impact has higher forces than a soft impact. And it is not always possible to calculate the hardness of the impact, and the resulting forces.
i can't find definite answer from this thread. (sorry but on my perspective people are complicating a simple question)
 
  • #13
Chandrasekar said:
i can't find definite answer from this thread.
There wasn't an answer in that thread. There were about 700 different attempts to get the first poster to realise that he had a contradictory mental model of how a crash happened, but no resolution.
Chandrasekar said:
sorry but on my perspective people are complicating a simple question
As they say, "to every question there is an answer that is both simple and wrong". This is one where there is no simple right answer.

This is basically why crash test dummies exist - there isn't a way of working out forces during a car crash except to build a car and slam it into a wall and see what happens. You might be able to build a computer model these days, but I would suspect anything that isn't a cuboid of perfectly elastic material landing flat on one face isn't tractable analytically.
 
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FAQ: How to Calculate force exerted on a falling body?

1. What is the basic formula to calculate the force exerted on a falling body?

The basic formula to calculate the force exerted on a falling body is F = m * g, where F is the force, m is the mass of the object, and g is the acceleration due to gravity (approximately 9.81 m/s² on Earth).

2. How does air resistance affect the force exerted on a falling body?

Air resistance opposes the motion of the falling body and reduces the net force acting on it. The actual force exerted on the body is the gravitational force minus the air resistance. As the velocity of the falling body increases, the air resistance also increases until it balances the gravitational force, leading to terminal velocity where the net force is zero.

3. What is terminal velocity and how is it related to the force on a falling body?

Terminal velocity is the constant speed that a freely falling object eventually reaches when the resistance of the medium through which it is falling prevents further acceleration. At terminal velocity, the force of gravity is balanced by the force of air resistance, resulting in a net force of zero and no further acceleration.

4. How can I calculate the force exerted on a falling body if I know its terminal velocity?

If you know the terminal velocity (v_t), you can calculate the force of air resistance (F_r) at terminal velocity using the equation F_r = m * g, where m is the mass of the body and g is the acceleration due to gravity. Since at terminal velocity, the forces are balanced, F_r equals the gravitational force.

5. Does the shape and surface area of a falling body affect the force exerted on it?

Yes, the shape and surface area of a falling body significantly affect the force exerted on it due to air resistance. A larger surface area increases air resistance, reducing the net force and slowing down the acceleration. Streamlined shapes experience less air resistance compared to objects with larger, irregular shapes.

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