Collect a large empty beer or soda can.
Heat it in a stove with a few table spoons of water in the can.
Keep a dish with ice water on the side.
The water should be enough to make a seal with the top of the can.
Heat the can until it starts emitting steam. Use a thong to grab the can and invert it in the dish.
You will notice that the can gets squished. Heating the can causes the air inside to expand.
The air is cooled rapidly when placed in the cold dish.
The air inside shrinks creating a region of low pressure.
The pressure around the can is greater. It pushes the walls of the can causing it to crush. This also shows pressure acts equally in all directions.
Take two balloons and fill them with air. Tie a piece of string to each of them.
Hold the balloons with both hands at a nose level. Blow hard between the balloons and watch their movements.
They should move towards each other. This is because blowing increase the speed of air between the balloons.
This reduces the air pressure in between significantly.
The air around the balloons possess less speed thus more pressure.
The pressure difference pushes the balloons together.
Take a jar and put it in position.
Blow air into a balloon until it’s a bit larger than the opening of the jar.
The size of the balloon should be such that it cannot be easily shoved into the jar.
Light a piece of paper and place it in the jar. Wait until the flame goes out.
Take the balloon by the string and lift it up.
The balloon should go with the jar. This is because the part of air that supports combustion gets consumed. This results to a drop in air pressure inside the jar.
The surrounding air pressure becomes greater thus pushing the balloon into the jar.
Ping Pong Funnel
Take a ping pong ball and insert it in a funnel.
Hold the funnel and blow hard. You can tilt your head to allow the ball end to point to the ceiling.
No matter how hard you blow, the ball remains in the funnel.
This is because blowing air throw the funnel where the ball sits reduces air pressure. The pressure around the ball is overwhelmed by the greater surrounding air pressure.
This pressure pushes the ball back into the funnel. This prevails no matter how hard you blow or hold the funnel.
Use your bottom lip to hold a piece of paper.
Blow hard across the sheet of paper.
You will notice that the sheet flies up. This is because blowing the piece of paper increases air speed on the upper side.
This results in a pressure drop.
The pressure on the lower side becomes greater.
The pressure difference forces the paper to lift upwards.
This is the same principle applied in airplane wings.
Take a glass and fill it a-third-way with water.
Cover the mouth of the glass with an index card.
Invert the glass over a sink while holding the card in place.
Gently, remove your hand from the card.
The card will remain in place.
This is because water is lighter than air. The card experiences an upward force from below. Water exerts a less force on the card allowing it to stay in place.
Fill a bottle halfway with water.
Take a long straw and insert it inside the bottle.
Wrap a lump of clay around the straw to form a seal.
Place the straw in your mouth and blow hard.
Stand back and watch.
You will notice that water moves up and out of the straw. This is because blowing air in the straw reduces air pressure. The greater air pressure inside the sealed bottle forces water to move up and out through the straw.