How fast objects fall through air

So its terminal velocity speed is much slower than a rock with the same weight. This is why an ant can fall off a tall building and land unharmed, while a similar fall would kill you. Keep in mind that this process happens in any gas or fluid.

So terminal velocity defines the speed that a rock sinks when you drop it in the water. But they can increase their speed tremendously by orienting their head towards the Earth — diving towards the ground.

But why do all objects free fall at the same rate of acceleration regardless of their mass? Is it because they all weigh the same? These questions will be explored in this section of Lesson 3. In addition to an exploration of free fall, the motion of objects that encounter air resistance will also be analyzed.

In particular, two questions will be explored:. As learned in an earlier unit, free fall is a special type of motion in which the only force acting upon an object is gravity.

Objects that are said to be undergoing free fall , are not encountering a significant force of air resistance; they are falling under the sole influence of gravity. Under such conditions, all objects will fall with the same rate of acceleration, regardless of their mass.

But why? Consider the free-falling motion of a kg baby elephant and a 1-kg overgrown mouse. If Newton's second law were applied to their falling motion, and if a free-body diagram were constructed, then it would be seen that the kg baby elephant would experiences a greater force of gravity. This greater force of gravity would have a direct effect upon the elephant's acceleration; thus, based on force alone, it might be thought that the kg baby elephant would accelerate faster.

But acceleration depends upon two factors: force and mass. The kg baby elephant obviously has more mass or inertia. This increased mass has an inverse effect upon the elephant's acceleration.

The gravitational field strength is a property of the location within Earth's gravitational field and not a property of the baby elephant nor the mouse. All objects placed upon Earth's surface will experience this amount of force 9. Being a property of the location within Earth's gravitational field and not a property of the free falling object itself, all objects on Earth's surface will experience this amount of force per mass.

As such, all objects free fall at the same rate regardless of their mass. Because the 9. Gravitational forces will be discussed in greater detail in a later unit of The Physics Classroom tutorial. Here you go. Click the pencil icon to see and edit the code, and click Play to run it.

View Iframe URL. You can see that the ping-pong ball almost reaches a constant speed after dropping a distance of 10 meters. I put a "no air" object in there for reference. If you want to see what happens if you change the massgo ahead and change the code and re-run it. It's fun. Now we get to the interesting question. If I drop two objects from the same height, does the heavier one hit the ground first? The answer is "sometimes. Drop 1: A basketball and bowling ball.

Here is a slow-motion view of this actual thing. If you ignore air resistance, then these two objects have the same acceleration, because they have different masses see above. But why can you ignore the air resistance in this case? Looking at the basketball, it has a significant mass and size. However, it is moving fairly slowly during the fall. Even at the fastest part of this drop the force from air on the ball is super tiny compared to the gravitational force.

Now, if you dropped it from a much higher starting point, the ball would be able to get up to a speed where the air drag makes it fall slower than the bowling ball. Drop 2: A small ball and a cardboard box top. Just to be clear, the mass of the cardboard is WAY higher than the ball. Here is the drop. Sorry, the ball is hard to see since it's small. Does the more massive object fall faster? In fact it's the lower mass that hits the ground first.

It's not just mass that matters; size matters too. This produces a significant air resistance force to make it hit the ground later. Drop 3: Two pieces of paper. Two sheets of paper are pretty much the same, so they should have the same mass. However, they can hit the ground at different times.

I tricked you. Both papers have the same mass, but I crumpled one up, so they have different surface areas. The crumpled-up paper hits the ground first. It seems like this could be a good party trick. But again, it's about more than just the mass of the object. Two people jump out of an airplane with parachutes, because they aren't crazy. One person is large, and one person is small.

Which one falls with the greatest terminal velocity? Yes, you can assume they are both in standard free fall position same shape. I am going to invoke the "spherical cow" principle and look at two falling spherical humans instead. Human 1 is a sphere with a radius of 1 meter yes, that would be huge , and human 2 has a radius twice as big, at 2 meters.

How do the gravitational forces on these two spherical humans compare? Human 2 is obviously heavier. If the human density is constant, then the increase in gravitational force will be proportional to the increase in volume.

If you double the radius of a sphere, you increase the volume by a factor of eight volume is proportional to radius cubed. So human 2 has a weight eight times that of human 1.

What about the air resistance on these two humans? Again, human 2 will have a bigger area and more air resistance. If you double the radius, the cross-sectional area will be four times as much since area is proportional to radius squared. Now you see that the bigger human will have a greater terminal velocity. Human 2 has a weight that is eight times as much, but air drag that is only four times as much as the smaller human.

Now let's take this to the extreme. An ant and an elephant jump out of a plane. The elephant is going to need a massive sized parachute, but the ant probably doesn't need anything. Since the weight-to-area ratio is super tiny for a super tiny object, the ant will have a very small terminal velocity. It can probably impact the ground with little injury. Note to my ant readers: Please be safe and don't try this in real life, in the unlikely event that I am wrong.

I think this might be my longest blog post. Congratulations if you made it all the way to the end. Falling without air resistance. But does the gravitational force decrease with height? Rhett Allain is an associate professor of physics at Southeastern Louisiana University. He enjoys teaching and talking about physics. Sometimes he takes things apart and can't put them back together.