This may sound dumb to some folks, but lets say I fire a gun. 1000N of force goes into the bullet, and another 1000N of force goes into my body. Even if i strap the gun to the ground, it will just apply 1000N of force to move the earth by a tiny amount. Because of this, does it mean that it isn’t possible to have 2000N of force going to the bullet with the same parameters as before?
In: Physics
I hate the way physics is taught. *None* of that 1000N goes into moving the Earth. In an ideal world, yes. But in reality, it might dig the gun into the ground, where the energy gets used compacting the soil or whatever. Zero of it moves the planet
Everyone is giving complex answers, but you are basically correct, you cannot capture all the force in one direction.
Yes.
Though it doesn’t actually have to be wasted. Some of the recoil energy can be used for operating reloading mechanisms so you can use more than half the energy.
Newton’s third law says that all force is equal and opposite, and force is mass times acceleration. So the mass-times-acceleration applied to the bullet will be equal to the mass-times-acceleration applied to the gun/shooter.
Because the mass of the gun (plus shooter) is many many times more than the mass of the bullet, the acceleration to the bullet is much much greater than the acceleration to the gun. And so most of the energy (but admittedly not all) goes to the bullet.
The energy generated by burning the gunpowder is indeed not 100% converted into accelerating the bullet (kinetic energy). No matter how hard you strap down the gun this will not change…
But by strapping down the gun you can change the proportion of kinetic energy that goes into the bullet in relation to how much of it goes into moving the gun.
Compare it to trying to push a block of concrete while standing on a slippery surface. When you try to push the block, you actually push yourself (or your feet) back.
Now because the bullet has less mass than the gun, it takes more energy to move the gun. Therefor the bullet is always going to accelerate faster than the gun. So strapping the gun down wont double the speed of the bullet.
There will be some wasted energy, there always is, but not as much as you think.
Your math is missing mass and density. You become a wall and the force getting sent at you returns in the bullets direction.
No. You seem to be thinking about momentum rather than kinetic energy.
When you do that, the change in *momentum* of the bullet will be equal and opposite of that of the Earth, but the bullet will have nearly all of the kinetic energy.
Momentum is (mass)*(velocity)
Kinetic energy is (1/2)*(mass)*(velocity)^2
Because of the squared velocity term in the kinetic energy, if two objects have the same momentum, the smaller and faster one will have more kinetic energy than the slow heavy one.
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