Tag Archives: Vacuum

Gravity Falling Experiment: Feather in a Vacuum!

Galileo once proposed that all objects under gravity, whether they’re really heavy or really light, will fall and accelerate downwards at the same rate. In a famous experiment, he supposedly dropped both from the Leaning Tower of Pisa and proved it. 


Why is this true? For something with more mass, it does feel a stronger downward force from gravity.

BUT because of the mass, it’s harder for that thing to accelerate. (When you hear “accelerate,” think rate of falling).  So for something relatively heavy, the stronger pull of gravity and the toughness to accelerate it should perfectly balance each other out, causing things accelerate at the same rate. This fact is sometimes referred to as Newton’s 2nd Law. 

The problem with this explanation is that it seems to defy what we see every day, right? 

We dropped a penny and feather at the same time. You probably don’t need to do this experiment to guess what happens. The penny will hit the deck long before the feather. 

Feather Accelerating Different Rates

It’s not that Galileo and Newton are wrong, it’s just that their model is simple; it doesn’t take the full picture into account. The secret here is that Newton’s 2nd Law only holds true if gravity is the ONLY force acting on the two objects. If objects fall through the air, then air resistance plays a part. And of course, some objects are more affected by air resistance, like feathers. To design a better experiment, we could try the same objects, but get rid of the air! We’ll use a vacuum chamber.

get rid of the air vacuum

A vacuum chamber will suck out some air, creating less air resistance. The less air there is, the closer their rate of falling is! 

Vacuum Falling Rate Comparison

If you had no air at all, if you could truly get gravity to be the sole factor, then you could call the object being in free-fall, and you would prove Newton’s 2nd law true. For this reason, the feather experiment was re-created on the Moon by astronaut David Scott using a feather and a hammer. It works because yes, our Moon has gravity (because it has mass) but it doesn’t really have air resistance, because there’s basically no atmosphere. 

David Scott Feather Experiment

How about that? 

Written By: Amanda Williams

Build Your Own Vacuum in Four Steps

All you need for this at-home science is a glass, a plate, a candle, water, a match, and a bit of caution, because we are dealing with fire.

Step 1: Pour the water on the plate

Step 2: Place the candle on the center of the plate

Step 3: Light the candle (or have a guardian light it for you)

Step 4: Place the glass down over the candle, step back and watch science happen!

This experiment is all about maintaining an equilibrium of air pressures inside and outside the glass.  We usually experience air pressure as the force from the atmosphere pushing down on us. Here at AstroCamp we feel about twelve PSI, or pounds per square inch, of force which is the same amount of force that the water on the plate initially feels.

The flame heats up the air on the inside, creating a higher pressure than the air on the outside. Hotter air has a higher energy and therefore exerts more air pressure.  The higher pressure pushes the water down and out of the glass. You should be able to see air bubbles in the water just outside of the glass from the air forcing the water out.  

Fire needs oxygen in order to continue the combustion process in the glass, but because we trapped air in the there is only a finite amount.  When the flame uses up all of the oxygen it goes out, which allows the air to cool.  Cold air doesn’t have as much pressure as hot air and has less pressure than the air outside of the glass.  Therefore the air on the outside of the glass pushes with greater force on the water than the air on the inside so the water is able to get sucked back up into the glass!  When the water level evens out that is  when you know you have reached an equilibrium of air pressures again.


Modeling Outer Space

You’re carrying an awful lot of weight right now. It’s hard to tell, but every square inch of you is supporting fifteen pounds of atmospheric pressure! Multiply that by the number of square inches on the surface of a human body, and you’ll find you’re bearing a hefty load.


Atmospheric pressure results from the weight of the air above you. Credit: Peter Mulroy, http://peter-mulroy.squarespace.com/air-pressure/

Our senses don’t usually register atmospheric pressure because it’s part of our natural habitat. It’s easier to observe the significance of the air around us by removing it and seeing what happens. You don’t know what you’ve got until it’s gone! The vacuum chamber is the perfect tool for exploring atmosphere-free science.

One of the most telling differences between solid, liquid, and gaseous states is the way each one occupies space. A solid object keeps both its size and its shape, no matter where you set it down. A liquid changes shape to match the container that holds it, but still takes up a fixed volume of space.  Gases follow no such rules. The molecules in a gas will spread out indefinitely, filling any space available. We can observe this by trapping some gas in a stretchy container and exposing it to vacuum conditions.


At the microscopic level, a marshmallow is a sugar-and-gelatin sponge full of tiny air pockets. In other words, it’s a stretchy (and delicious) container with gas trapped inside! When we remove the air around the marshmallow, the gas within expands to fill the surrounding vacuum. The bubbles stretch bigger and bigger until they pop and the air escapes. When the air returns, there is nothing inside the tiny bubbles of the marshmallows, so they shrink back down below their original size.

Water is another interesting low-pressure test subject. By removing the air nearby, we effectively lift fifteen pounds of weight from each square inch of the water’s surface. This does not mean that the water is getting hotter. Instead, the drop in pressure brings the boiling point of the liquid down below room temperature.


Water in a vacuum evaporates rapidly at room temperature. Newly formed water vapor condenses on the inside of the chamber, running down in droplets.


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