# Explaining Why a Bullet Hits Lower than a Laser Beam

• kirsten_2009
In summary: If you throw the rock hard enough it will get there before the feather.In this case, we have two bullets, one with a small mass and one with a large mass. We throw them at the same speed. The heavier bullet is going to get there first, right? Because it has more inertia and will "shrug off" the effects of air resistance better than the lighter bullet.So...is this the concept of 'terminal velocity'?In summary, the two objects experience the same downward acceleration due to gravity, but the object with less mass will experience more air resistance and thus fall slower. In the case of the bullet and the laser beam, the bullet, being heavier, will experience more air resistance and hit
kirsten_2009

## Homework Statement

A riffle barrel and a laser point directly towards a target some distance away. General relativity says that the bullet and the light experience the same downward acceleration during horizontal travel, yet the bullet hits the target well below the laser beam. Explain.

## The Attempt at a Solution

While the downward acceleration is acting on both the bullet and the laser beam at the same rate; this downward acceleration actually has more time to work on the bullet that on the laser beam since the laser beam is traveling a lot faster (speed of light) than the bullet. Also, the bullet has more mass to be acted on downward than the laser beam. Consequently, the laser beam will arrive faster to the target as it has less time and mass to be acted on by downward acceleration forces compared to the bullet and the added downward forces experienced by the bullet will drag it down; hitting the target after and below that of the laser beam...correct?

Thanks for the help :)

kirsten_2009 said:
While the downward acceleration is acting on both the bullet and the laser beam at the same rate; this downward acceleration actually has more time to work on the bullet that on the laser beam since the laser beam is traveling a lot faster (speed of light) than the bullet. Also, the bullet has more mass to be acted on downward than the laser beam. Consequently, the laser beam will arrive faster to the target as it has less time and mass to be acted on by downward acceleration forces compared to the bullet and the added downward forces experienced by the bullet will drag it down; hitting the target after and below that of the laser beam
You have advanced two arguments, one based on time and one based on mass. One is right, one is wrong. Can you identify which and why? Hint: Pisa.

Hello!

Thanks for the reply. I've been thinking about it...and the time one has to be right since the difference in speed of the two traveling objects is so significant. Mass has to be wrong because it wouldn't be of importance in outer space which is where I assume this is taking place...right?

kirsten_2009 said:
Hello!

Thanks for the reply. I've been thinking about it...and the time one has to be right since the difference in speed of the two traveling objects is so significant. Mass has to be wrong because it wouldn't be of importance in outer space which is where I assume this is taking place...right?

Why would it be taking place in outer space?

You could think about two rifles: one fires a large, heavy bullet; the other a smaller bullet. Imagine they fire their bullets at the same speed. What can you say about the tracetory of the two bullets?

Hmmm...well if this was happening here on Earth...(I just automatically assume every thought experiment happens in outer space because my textbook never deals with stuff on Earth)...the heavier bullet would hit the target lower than the smaller bullet...so speed has nothing to do with it?

kirsten_2009 said:
Hmmm...well if this was happening here on Earth...(I just automatically assume every thought experiment happens in outer space because my textbook never deals with stuff on Earth)...the heavier bullet would hit the target lower than the smaller bullet...so speed has nothing to do with it?

So, you've never heard of poor Galileo climbing all the way to the top of the leaning tower of Pisa to demostrate that a heavy object and a light object fall at the same rate?

No...actually, I haven't. I thought however, that two objects of different mass fell at the same rate in a vacuum...so this also holds true in "real life"?

kirsten_2009 said:
No...actually, I haven't. I thought however, that two objects of different mass fell at the same rate in a vacuum...so this also holds true in "real life"?

Yes. It's true for all objects in a vacuum. The complication in "real life" is air resistance. Similar objects (same density and shape) will fall with the same acceleration. Normally you would think of a light object (feather) falling more slowly than a heavy object (canonball). But, take a woman with an open parachute. She's heavier with the parachute than without it, but falls more slowly. In this case, the heavier object falls more slowly.

In general, unless the effects of air resistance are significant, objects accelerate at the same rate due to gravity. So, in real life, the trajectory of a bullet is not dependent on its mass.

kirsten_2009 said:
two objects of different mass fell at the same rate in a vacuum
Quite so, but how does that lead you to conclude
kirsten_2009 said:
the heavier bullet would hit the target lower than the smaller bullet
?

Hello,

Thanks for the excellent explanation! I think my confusion arose from the fact that the conditions in a vacuum are different than in "real life" since I figured the heavier bullet would have more 'drag' (if that's even the appropriate term) since it was heavier...but I see what you guys are saying. Thanks as always for the help! :)

kirsten_2009 said:
the heavier bullet would have more 'drag'
It generally would, but in proportion to its inertia less drag than the lighter bullet. So in air the lighter bullet would hit the target lower. Imagine throwing a rock at a target, then throwing a feather.

## 1. What causes a bullet to hit lower than a laser beam?

A bullet is affected by a force called gravity, which pulls it down towards the ground. This is known as bullet drop or bullet trajectory. On the other hand, a laser beam travels in a straight line, unaffected by gravity.

## 2. Is there a difference in velocity between a bullet and a laser beam?

Yes, there is a significant difference in velocity between a bullet and a laser beam. A bullet travels at a much slower speed than a laser beam, which is essentially the speed of light.

## 3. Can the distance from the target affect the difference in impact between a bullet and a laser beam?

Yes, the distance from the target can play a role in the difference in impact. Because of the slower velocity of a bullet, it can be affected by factors such as wind and air resistance, which can cause it to deviate from its intended trajectory. A laser beam, on the other hand, travels in a straight line and is not affected by external forces.

## 4. Are there other factors besides gravity that can cause a bullet to hit lower than a laser beam?

Yes, there are other factors that can contribute to the lower impact of a bullet compared to a laser beam. These include the weight and shape of the bullet, as well as the type of firearm used to fire it. Additionally, human error and environmental conditions can also play a role in the accuracy of a bullet's trajectory.

## 5. How can we use this knowledge to improve firearm accuracy?

Understanding the difference between the trajectory of a bullet and a laser beam can help us make adjustments to improve firearm accuracy. This includes accounting for factors such as bullet drop and external forces, as well as practicing proper shooting techniques. Additionally, advancements in technology have led to the development of more accurate firearms and ammunition, helping to minimize the impact of these factors on accuracy.

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