# Building a wall to reduce maximum collision force

• axutio
In summary: Oh, okay. So you're thinking of using a buffer instead of springs?I am thinking of using a buffer instead of springs. A buffer is something that can provide a constant force, even when the springs are compressed. It can be something like a car body each end of the passenger section, or friction.
axutio

## Homework Statement

I was recently assigned a project of, tl;dr, building a wall to reduce the maximum force during a collision. Let me start by describing the setup as best as I can. First, here's an image:

These aren't the exact track and carts we're using, but they provide a great overview. These, however, are the exact type of carts being used:

So, imagine if the ramp from the first image was inclined at 50-60° and then the a force sensor was placed on the lower edge, such that the cart would be released from a length of about 80 cm on the angled track away from the force sensor to crash into the force sensor. The carts being used, by the way, are 0.5 kg and there is very minimal friction between the cart and track.

The project is essentially to build a wall in front of the force sensor - which can be up to 10cm in length and of any width/height as long as it does not touch the ramp and therefore use friction to slow the cart down. The goal is to release the cart in the aforementioned conditions and then to achieve the _lowest maximum force reading_ during the collision possible. The total impulse itself does not matter (which means, to my understanding, that elastic collisions would be no worse than inelastic collisions) as long as the lowest possible maximum force is achieved - my personal goal is a force under 8 Newtons.

There are a few caveats, and I'm going to try to explain all the rules in better detail here:

1. the wall is not allowed to touch the track itself, to prevent the intentional use of friction to slow the car down
2. I am allowed to attach things to the cart itself to a very limited extent; it has to be something that can be taken on and off easily and is not the main slowing mechanism - this cannot come into contact with the track either
3. use of any non-mechanical energy is not allowed - nothing electronic or chemical

## Homework Equations

The main equations relevant to this question are, as far as I can tell, the general momentum equations, such as J = FΔt, p=mv, and in addition the kinematic equations for further calculations. However, this question is mostly conceptual, so whereas equations can be used to check work and test ideas later on, at the moment, I am seeking ideas.

## The Attempt at a Solution

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So, here are some of the things I have already come up with:
1. I am thinking that a wall made entirely of somewhat soft springs that go the full 10cm would be ideal, as it would create a collision that would last for the longest time, and therefore would have the lowest force
2. I am also thinking of attaching a magnet to the rear end of the cart. I already discussed doing this to slow down the cart as the track is aluminum with someone else, but I was told to consider Eddy currents as a more important and stronger force - I have done some research into these, and while I can't say I really understand them, I do get the gist.
3. I am also thinking of attaching a thin but huge in length and width piece of cardboard above the cart, to use the air resistance against the cardboard to slow the cart down. I am unsure of how effective this would be.

I would appreciate any feedback any of you have to give, and I'm really sorry if this question is off-topic! Please let me know so I can copy it to somewhere where it might be more acceptable. Thanks again!

berkeman
axutio said:
the wall is not allowed to touch the track itself, to prevent the intentional use of friction to slow the car down
So what would the wall be attached to? What if that had a frictional connection to the wall?
axutio said:
I am thinking that a wall made entirely of somewhat soft springs
The trouble with springs is that they do not provide a constant force. The force increases as the spring compresses. That is why it is generally preferred to use a buffer that crumples (car body each end of the passenger section) or friction.

haruspex said:
So what would the wall be attached to? What if that had a frictional connection to the wall?

The trouble with springs is that they do not provide a constant force. The force increases as the spring compresses. That is why it is generally preferred to use a buffer that crumples (car body each end of the passenger section) or friction.

There's a board on top of the force sensor, and the wall is attached to that.

I get what you mean with springs. Could you expand a bit on using friction?

axutio said:
There's a board on top of the force sensor, and the wall is attached to that.

I get what you mean with springs. Could you expand a bit on using friction?
If the wall is mounted on rails parallel to the track, but with some grip, the retarding force will equal the kinetic frictional force, so remain more or less constant during the motion.

One possibility might be to build a wall containing a dash pot (aka damper). This could be a simple EPS "piston" in cardboard tube arrangement. If you provide a hole for air to escape then the size of the hole could be adjusted to optimise the system for minimum impact force.

If you have info about the track can you calculate the velocity at impact. Then if you were to assume the wall sets the maximum stopping distance you could estimate the likely minimum impact force to see if your target is feasible.

## 1. How does building a wall reduce maximum collision force?

When a wall is built, it acts as a barrier between two objects. In the case of reducing maximum collision force, the wall acts as a buffer or cushion, absorbing some of the energy from the collision and reducing the force that is transferred to the objects involved.

## 2. What materials are best for building a wall to reduce maximum collision force?

The best materials for building a wall to reduce maximum collision force are those that are strong, durable, and have the ability to absorb impact. Some common materials used for this purpose include concrete, steel, and reinforced materials such as rubber or foam.

## 3. Can building a wall completely prevent collisions?

No, building a wall cannot completely prevent collisions from occurring. However, it can significantly reduce the impact and force of a collision, potentially minimizing damage and injuries.

## 4. Is building a wall the only solution for reducing maximum collision force?

No, building a wall is not the only solution for reducing maximum collision force. Other measures such as speed bumps, warning signs, and traffic control devices can also help to reduce the force of collisions.

## 5. How can I determine the appropriate height and thickness for a wall to reduce maximum collision force?

The height and thickness of a wall for reducing maximum collision force will depend on various factors such as the speed and weight of the potential colliding objects, the angle of impact, and the materials used. It is important to consult with a structural engineer to determine the appropriate dimensions for a wall based on the specific needs of the location.

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