# Pressure

By Kate Fraser on Feb 07, 2014

Purpose:

To encourage students who are blind or visually impaired to discover if there is a relationship between depth and pressure

Background Information:

Pressure can be felt, not seen. The results of pressure can be seen but also observed tactually. The amount of force acting on a unit of area is called pressure. Pressure is equal to force divided by area. Pressure can be changed by changing the force. When the area of applied pressure stays the same, increasing the amount of force will increase the pressure.

Pressure can also be changed by changing the area in which the force is pushing. If you apply the same amount of force to a larger area, the pressure is decreased. Pressure can also be found and felt in nature.  When pumped into a tire or a balloon, air exerts pressure to keep the item inflated.  The air pressure in a tire can be great enough to support the weight of a truck. The pressure exerted by moving air, or wind, can turn the vanes of a windmill or keep a kite flying.  The pressure exerted by a volume of water can cause water to flow a grater distance.

## Preparation:

These activities are a good introduction to pressure. Press a pencil point gently against a piece of clay.  The point of the pencil will make a small dent in the clay.  If pressed a little harder, the force and the pressure increase.  The pencil point will sink deeper into the clay.

Gently press an unsharpened pencil against the clay with the same force used before, the pencil will barely make a mark on the clay.  Increase the force; the flat pencil will dent the clay but will not sink into the clay as far as the pencil point did.  This shows that the pressure applied with the flat, unsharpened pencil is less than the pressure applied with the sharp point of the pencil.

It's beneficial to practice measuring accurately in centimeters before carrying out the activity.

## Materials

• Milk carton or plastic soda bottle
• Adapted metric ruler or tape measure
• Tape
• Basin for water
• Safety goggles
• Apron
• Modeling clay
• Something with which to record your observations

## Procedure

1. Put on safety goggles and aprons.
2. Make a hole in the milk carton about 5cm from the bottom.
3. Plug the hole with modeling clay.
4. Make a hole in the milk carton about 15cm from the bottom
5. Plug the hole with modeling clay.
6. Fill the milk carton with water
7. Predict what will happen when the clay plug at the 15cm hole is removed.
8. Place the carton in a basin and remove the clay plug at the 15 cm mark.
9. As soon as the clay plug is released, have a partner mark the location of the end of the stream with a piece of water proof tape on the basin. Measure the distance and record.
10. Re-plug the hole and fill the carton with water again.
11. Predict what will happen when you remove the clay from the 5cm hole.
12. Repeat step 9 for the 5 cm hole.
13. Compare your data and make observations

Resources

This activity was adapted by Michele Engelbrecht and Kate Fraser from Concepts and Challenges: Physical Science, Fourth Edition. Parsippany, NJ: Globe Fearon Inc., Pearson Learning Group, 2009, pages 260 to 261.