Y9 Bream Homework

Pressure

1. Why do stiletto heels damage floors?
Stiletto heels have a very small surface area. As a result the person’s weight is spread over a small area and there is high pressure exerted on the floor

2. Why is thick padding added to the straps of some rucksacks?
The padding increases the area of the straps. The weight of the rucksack is spread over a larger area. This reduces the pressure exerted on the person’s shoulders.

3. Why do bulldozers have caterpillar tracks?
This increases the area in contact with the soft ground. The large weight of the bulldozer is spread over a larger area so there is less pressure and the bulldozer is less likely to sink into the mud.

4. Why do loaded plastic shopping bags dig into your hands?
The surface area in contact with your hand is small. The weight of the shopping in the bag is concentrated over a small area so the pressure on your hands is high

5. Why do knives cut?
The blade of a knife has a small area. When you push down on the knife the force is concentrated on a small area. This produces a very large pressure under the blade.

6. What do you do when you sharpen knives?
The area under the blade is made smaller increasing the pressure exerted by a force of the same size.

7. Why must workmen walk on ladders on top of a weakly constructed roof?

The area of the ladder in contact with the roof is large. This spreads out the weight of the workman exerting a low pressure on the roof.

8. Why do some heavy lorries have 8 rear wheels?
The weight of the lorry is spread over a lager area exerting a lower pressure on the road

9. Why can an Indian Fakir lie on a bed on nails if it contains a large
number of nails ?
The surface area of a large number of nails is high. The weight of the fakir is spread over a large surface area. The pressure exerted by each single nail is low.

10. Why is it less painful for small children to walk barefoot on pebbles than it is for adults?

The child weighs less than the adult. As a result the pressure exerted by a single pebble of the same area is lower on the foot of a child than the foot of an adult