Continuing our Science for Kids series, Dr. Naomi Lavelle, from Dr How’s Science Wows tells us all about pressure and how to explain “what is pressure?” to your child, with 3 fun, easy pressure experiments for kids to try.
What is Pressure?
Pressure is force applied over a certain area!
Air Pressure is the force pushing on us by tiny particles in the air (air molecules). Water Pressure is the force exerted by water on its surroundings.
Air molecules are pushing against our bodies all the time but we are so used to it that we are not aware of the feeling. The air pressure we are used to at sea level is about 15 pounds per square inch (15 p.s.i).
When the atmosphere is pressing down with a lot of pressure we call it High Pressure, when it is pressing down with less force we call it Low Pressure. Air pressure is higher at sea level and becomes lower as we go higher up in the atmosphere.
So why do our bodies not get squashed by all the air molecules pushing against us?
The reason is that we have air in our bodies too and this air is pushed outwards with the same force as the air pushing in on us!
Did you know… as there is no air in outer space astronauts have to wear pressurised space suits which create the same force on their bodies as the air pressure on earth?
Pressure and the weather
Pressure is very important in determining the weather!
When the weather forecast predicts a high pressure system it means we will get a mass of cool dry air that should bring fairer weather and lighter winds. A low pressure system means warm, moist air with stronger winds and more stormy weather.
Weather forecasters usually measure air pressure with a Barometer!
When we watch the weather forecast the areas of high pressure systems are marked with a H. The areas of low pressure systems are marked with an L.
Pressure and flight
It is air pressure and the difference between high and low pressure that allows airplanes and birds to fly!
The wings of both birds and planes are shaped in such a way as to make the air travelling over the top of the wing move faster – this creates low pressure at the top of the wing and high pressure below the wing. The high pressure pushing up on the wing is stronger than the low pressure pushing down on it so the wing is held up in the air!
Did you know… the reason our ears pop when we are in an aeroplane is because the air in our bodies is adjusting to the change in air pressure from high to low as the aeroplane rises?
3 Fun Pressure Experiments to Try
#1. Testing Water Pressure!
You will need… an empty plastic bottle (1 or 2 Litre), a thumbtack, cellotape or duct tape.
What to do… carefully make a number of holes (about six) up the side of the plastic bottle – using the tumb tac (or ask an adult to help). Make the holes one above the other, leaving about an inch between each hole. Now cover the holes with one strip of tape. Fill the bottle to the top with water. Sit the bottle beside the sink with the taped side facing in to the sink. Remove the tape and look at the streams of water that escape from each hole!
So what is happening?… water pressure increases the deeper we go so the force of pressure near the water at the top hole is less than the pressure on the water below it. This means that the water coming out each hole travels further than the one above as it is under more pressure!
#2. Testing Air Pressure!
You will need… an empty plastic bottle (1 or 2 Litre), a balloon, a needle or thumbtack.
What to do… put the balloon inside the empty bottle and fold the neck of the balloon over the neck of the bottle. Now try blowing into the balloon to inflate it inside the bottle… what happens? Now make a hole in the side of the bottle with the thumbtack (or ask an adult). Try blowing up the balloon again – what happens this time?
So what is happening?… even though we cannot see air it has a weight and takes up space! When you blow in the balloon the first time the pressure of air on the balloon from inside the bottle stops you from blowing up the balloon. When you make a hole in the bottle the air can now escape, allowing air into the balloon!
Note: You can turn this into a fun trick using two bottles -one with a hole in the side and one without. Hand the one without the hole to someone to try while you use the other bottle!
#3. Or turn it into a water fountain!
What to do… blow up the balloon inside the bottle again but this time cover the hole with tape once the balloon is inflated! Now bring the bottle outside and pour water into the balloon using a jug, until it is full. When you are ready, remove the tape from the hole in the bottle and watch as your water fountain erupts!
Did you try one of the experiments? How did you get on? Tell us in the comments below!