GRADE FIVE SCIENCE
Hello Boys and Girls,
Have you been enjoying your holidays? Have you been reading and having fun? Ensure that you help your parents as well. We have been looking at air, air and its composition, air and burning and so on. This week we will continue to look at air. Let’s look at air and pressure.
We don’t think about it, but we are actually living at the bottom of a large pool of air. This air is called the atmosphere and is made up mostly of gases. These gases are colourless and odourless.
The weight of all the air weighing down on us is air pressure. Pressure is quite complicated but the best way to describe it is, as was mentioned, the weight of the air. So pressure is the amount of weight the atmosphere presses down on the earth’s surface. The more air that is above us, the higher the air pressure. At the top of mountains the pressure will be lower than at sea level.
Air pressure is one of the most important factors that determine what the weather is like. The ordinary pressure of the air surrounding us is 14.7 pounds per square inch, but the pressure can change when the wind blows or an object, like a car or airplane, accelerates.
One important principle to remember is that wherever the air pressure is higher, there will be a stronger force or push against an object. It’s also helpful to know that when an air particle speeds up, it actually “pushes” less. Imagine that fast-moving air particles are in so much of a hurry that they don’t have time to apply force. This principle is used in airplane wings to make planes fly. When a plane moves along the runway, the air above the wing speeds up more, lowering the pressure, so that the air below the wing can push the plane upward.
Do you want to see if these principles really work? Great! Try some or all of the following experiments:
Try this experiment over a tub or sink. i. Fill a plastic cup with water (in such a way that water runs out over the edges).
ii. Place a piece of still cardboard firmly over the cup. (There should be no space for air to pass.)
iii. Hold the cardboard in place and then turn the cup over.
iv. Gently remove your hand without disturbing the cardboard. v. Put the cup at several angles What do you think will happen?
Because of the atmospheric pressure, the cardboard will not fall down.
The ordinary pressure of the air surrounding us is 14.7 pounds per square inch, but the pressure can change when the wind blows or an object, like a car or airplane, accelerates.
One important principle to remember is that wherever the air pressure is higher, there will be a stronger force or push against an object. It’s also helpful to know that when an air particle speeds up, it actually “pushes” less. Imagine that fast-moving air particles are in so much of a hurry that they don’t have time to apply force. This principle is used in airplane wings to make planes fly. When a plane moves along the runway, the air above the wing speeds up more, lowering the pressure, so that the air below the wing can push the plane upward.
Do you want to see if these principles really work? Great! Try one or more of the following experiments: Water Glass Trick. Fill a cup one-third with water. Cover the entire mouth with an index card. Holding the card in place, take the cup to the sink and turn it upside down. Remove your hand from underneath. Voilà! Because the water inside the cup is lighter than the air outside, the card is held in place by about 15 pounds of force from the air pushing up, while the force of the water pushing down is only about one pound of force.
Fountain Bottle. Fill a 2-liter soda bottle half full of water. Take a long straw and insert it in the mouth. Wrap a lump of clay around the straw to form a seal. Blow hard into the straw—then stand back. Your blowing increases the air pressure inside the sealed bottle. This higher pressure pushes on the water and forces it up and out the straw.
Ping-Pong Funnel. Put a ping-pong ball inside the wide part of a funnel and blow hard into the narrow end. Why doesn’t the ball pop out? As you blow into the funnel, the air moves faster and lowers the air pressure underneath the ball. Because the air pressure is higher above the ball than below it, the ball is pushed down into the funnel—no matter how hard you blow or which direction you point the funnel.
The Million Dollar Bet. Take an empty water or soda bottle and lay it down horizontally on a table. Roll a piece of paper towel into a small ball about half the size of the opening. Tell a friend you’ll pay $1 million if he or she can blow the ball into the bottle. Don’t worry about losing money because this is impossible. No matter how hard someone blows to try to force more air into the bottle, there’s no room for it, so it will flow right out, pushing away the paper ball.
Kissing Balloons. Blow up two balloons and attach a piece of string to each. Hold one balloon by the string in each hand and position the two balloons so that they are at your nose level and 6 inches apart. Blow hard into the space between the balloons. This lowers the air pressure. The pressure of the surrounding air is now higher and it will push the balloons together.
Did you have lots of fun? Did you work with others?
Air is really fascinating to investigate. Don’t you agree? Until next week, goodbye Boys and Girls !