Forces extra for triple science

Question 1

What is upthrust?

Answer 1

An object that is partly, or completely, submerged experiences a greater pressure on its bottom surface than on its top surface. This causes a resultant force upwards. This force is called upthrust.

Question 2

Explain what happens to make an object sink in a fluid

Answer 2

If the density of the object is greater than the density of the fluid, the object can never displace enough fluid to create an upthrust that will hold its weight up so it sinks.
So if the weight of the object is more than the upthrust it will sink.

Question 3

Explain how an object floats in a fluid

Answer 3

If the density of the object is less than the density of the fluid, the object can displace enough fluid to create an upthrust that will hold its weight up so it floats.

Question 4

What is the equation for pressure in fluids?

Answer 4

Pressure (Pa) = Force exerted on a surface (N) / area (m2)

Question 5

Which states of matter are considered to be fluids?

Answer 5

Liquids and gases

Question 6

The pressure in fluids causes a force normal to a surface, what does this mean?

Answer 6

A force that is normal to a surface acts at right angles (90°) to it.

Question 7

Is the pressure in a liquid the same or different at different depths

Answer 7

Pressure increases as the depth increases.

Question 8

How do you calculate the pressure caused by a column of liquid ?

Answer 8

Pa = h x ρ x g

pressure (P) is measured in pascals (Pa)
height of column (h) is measured in metres (m)
density (ρ) is measured in kilograms per metre cubed (kg/m3)
gravitational field strength (g) is measured in newtons per kilogram (N/kg)

Question 9

What is the atmosphere of the earth?

Answer 9

The atmosphere is the layer of air around the Earth
- it is thin compared to the size of the Earth
- it becomes less dense as the altitude increases

Question 10

What causes atmospheric pressure?

Answer 10

Air molecules colliding with a surface cause atmospheric pressure

Question 11

What happens to the atmospheric pressure on an object as it rises above the ground?

Answer 11

Atmospheric pressure decreases as the height of a surface above ground level increases. This is because, as the altitude increases:

• the number of air molecules decreases
  - the weight of the air decreases
• there is less air above a surface

Question 12

Explain why an aircraft is pressurised when it flies at altitude

Answer 12

aircraft that fly at high altitudes must be pressurised because if the air pressure is too low, humans cannot take in oxygen quickly enough to meet their bodies’ needs.

Question 13

Describe a moment?

Answer 13

A force or system of forces may cause an object to turn. A moment is the turning effect of a force. Moments act about a point in a clockwise or anticlockwise direction. The point chosen could be any point on the object, but the pivot - also known as the fulcrum - is usually chosen.

Question 14

How is the magnitude of a moment calculated?

Answer 14

moment of a force = force × distance

This is when:

moment (M) is measured in newton-metres (Nm)
force (F) is measured in newtons (N)
distance (d) is measured in metres (m)  this is the perpendicular distance from the fulcrum to the load

Question 15

Describe what must happen with moments for a lever to be balanced

Answer 15

If an object is balanced, the total clockwise moment about a pivot is equal to the total anticlockwise moment about that pivot.

Question 16

There are 3 classes of lever. Identify the positions of the effort pivot and load for each and give a practical example

Answer 16

Class 1 lever effort - pivot - load see-saw, crowbar, scissors
Class 2 lever pivot - load - effort wheelbarrow, nutcracker
Class 3 lever pivot - effort - load tweezers, bicep curl

Question 17

Describe the difference between elastic and inelastic deformation.

Answer 17

elastic deformation is reversed when the force is removed
inelastic deformation is not fully reversed when the force is removed - there is a permanent change in shape