Eli5: what happens if an object is pushed past it’s terminal velocity?



Eli5: what happens if an object is pushed past it’s terminal velocity?

In: Physics

Nothing much. If whatever’s pushing it is removed, it will slow back down to its terminal velocity.

Terminal velocity is the point where air resistance and gravity cancel each other out. In your scenario, gravity is pushing less hard than air resistance (because it’s going faster than its terminal velocity), so it will slow down until it’s back in balance. Pretty much the same thing that happens as gravity speeds it up until air resistance stops it from speeding up any more, except with the two forces reversed.

Then it’s no longer in free fall.

To exceed terminal velocity, you’ll need an outside force to increase the speed of the object.

But it’s really not anything different than say an object moving horizontally at a speed greater than its terminal velocity.

For example, a 0.30cal bullet may have a terminal velocity of 300ft/s but it leaves the barrel of a gun at 2300 feet/s. A bullet traveling horizontally at 2300fps isn’t going to be different from a bullet traveling downwards at 2300 fps.

Nothing much. There would be a increase of friction and resistance but as long as the object can withstand the increases it will just go faster until the pushing force is removed then slow back down to its terminal velocity.

So you’ve got some accelerative force pushing it past its terminal velocity? Fine. Nothing much happens (unless you have some object that’s prone to falling apart in the wind). “Terminal velocity” just means the speed at which a falling object (accelerated down by gravity) is no longer accelerating, because of the upward force on it from air resistance. It does NOT mean some velocity that the object can’t move faster than, regardless of what forces act on it; only and nothing more than the velocity at which the force of air resistance equals the force of gravity. Bullets routinely exit gun muzzles at velocities (are pushed way past) they would never reach in free fall. Even water hoses can spray water droplets at speeds faster than falling rain. I don’t have data on the speed of water out of a super soaker. 🙂

Depends on *how much* it’s pushed past its terminal velocity. As others have mentioned, if it’s only pushed a little bit past the terminal velocity, then the object reaches a new point at which the forces balance, and then it stops accelerating again (and returns to terminal velocity once the extra force is removed.)

However, if it’s pushed waaayyyy past terminal velocity, the picture gets a lot more interesting, as illustrated by the [xccd relativistic baseball](https://what-if.xkcd.com/1/)

It moves faster, nothing else.

The faster something falls, the harder the atmosphere pushes back (it takes more energy to move the air away faster). Terminal velocity is simply the point where gravity and aerodynamics reach a balance. The amount of energy needed to move faster is greater than the potential energy of the object.

Increasing mass or decreasing air resistance would increase the velocity of the object. Skydivers tuck their arms against their sides to fall faster.

Short answer: air drag exceeds weight, causing it to slow down (unless thrust is supplied from somewhere.)