P11 - Pressure and Surfaces

Question 1

What is meant by a force?

Answer 1

A push or pull

Question 2

What is the definition for pressure?

Answer 2

Pressure is the force per unit area

Question 3

What is the equation for pressure?

Answer 3

Pressure = force (N) / Area(m^2)

Question 4

How do you calculate pressure due to liquids?

Answer 4

Pressure(Pascals-Pa) = height(m) x density(kg/m^3k) x gravity (N/kg or m/s^2)

Question 5

What is the air pressure caused by?

Answer 5

Air pressure is caused by the force of air molecules bumping into things.

Question 6

What is upthrust?

Answer 6

Upthrust is the upward force that a fluid (liquid or gas) exerts on a body (or object) floating in it.

Question 7

What is archimedes’ principle?

Answer 7

An object totally or partially immersed in a fluid is subject to an upward force equal in magnitude (size) to the weight of fluid it displaces.

Question 8

When does an object float?

Answer 8

An object floats when its weight is less or equal to the upthrust provided by the fluid. So the upthrust provided by the fluid acts with a greater force than the weight if the object.

Question 9

When does an object sink?

Answer 9

An object sinks when its weight is greater than the upthrust provided by the fluid, so there is a resultant force downwards.

Question 10

Explain how atmospheric pressure changes with elevation above sea-level.

Answer 10

The weight of the air is the force which causes the pressure, So with higher elevation, there are fewer air molecules above the unit area than the same area at lower heights, so there is a smaller weight, so less pressure.

Question 11

How do seatbelts reduce the impact felt?

Answer 11

Stretching increases the distance moved slightly, but extends the time taken more for passengers to stop. This decreases the rate of change of momentum and therefore reduces the force.

Question 12

How does the crumple zone reduce the impact felt?

Answer 12

It absorbs energy to deform and compact. It increases the time taken for the car to stop. This reduces acceleration and force on passengers

Question 13

How do air bags reduce the impact felt?

Answer 13

These inflate instantaneously upon a crash. Your head hits this and slows down. Increases the time taken for the head to stop moving. So reduces the force on the neck.