Paper 2 Forces

Question 1

What is a moment

Answer 1

The turning effect of a force

Question 2

Moment=

Answer 2

Force x distance moved

Question 3

Clockwise moments=

Answer 3

Anti-clockwise moments

W1 x D1 = W2 x D2

Question 4

How is the seesaw an example of the principles of moment

Answer 4

This states that for an object in equilibrium the sum of all clockwise moments about any point is equal to the sum of all anti-clockwise moment about that point

Question 5

What is the centre of mass of an object

Answer 5

The point at which the mass may though to be concentrated

Question 6

How can the centre of mass be found for symmetrical objects

Answer 6

Always lies along the line of symmetry of that object, if more that 1 line of symmetry, it’s where the lines cross

Question 7

How to find the centre of mass of an object in suspension

Answer 7

If you suspend object then release it it will soon come to rest. The centre of mass will be directly below the point of suspension. The object is said to be in equilibrium

Question 8

How do you find the centre of mass in an irregular shape

Answer 8

Shape is hung from a point and plumb line used to draw vertical line downwards from that pivot. The COM is somewhere along that point. This is repeated with the shape hanging from different points. Where they all intercept is the COM

Question 9

The stability of an object is affected by 2 factors

Answer 9

The width of the base of the object

The height of its centre of mass

Question 10

What is stable equilibrium

Answer 10

The centre of mass is raised as it is tilted (it tilts then falls back to the original position)

Question 11

What is unstable equilibrium

Answer 11

The centre of mass is lowered as it’s tilted (it tilts then falls over)

Question 12

What is neutral equilibrium

Answer 12

The centre of mass stays at the same level if it is pushed (it rolls)

Question 13

How do levers work

Answer 13

The greater the length of the lever from the pivot to the applied force, the easier it would be to lift the mass

Question 14

What is a force multiplier

Answer 14

A machine which allows small effort (input force) to move a larger load (output force);

Question 15

What is the mechanical advantage of a machine

Answer 15

The number of times the load moved is greater than the effort used

Question 16

Mechanical advantage=

Answer 16

load/effort

Question 17

In a force multiplier the mechanical advantage is…

Answer 17

Greater than 1

Question 18

In a distance multiplier the mechanical advantage is…

Answer 18

Less than 1

Question 19

What is the mechanical advantage of a lever if the distance from the pivot is 3x greater than the distance from the pivot to the load

Answer 19

Mechanical advantage is 3, the load is 3x heavier than the effort

Question 20

What is a distance multiplier

Answer 20

Take small movement of the effort and multiply it into a large movement of the load

Question 21

How are bicycles examples of distance multipliers

Answer 21

The gears of a bike are designed so that slow movement of the pedals produces a much faster rotation of the wheels

Question 22

Why do you use a low gear uphill in a car

Answer 22

Want a force multiplier, want output more than input

Question 23

Why do you use a higher gear downhill in a car

Answer 23

Want a distance multiplier, want output smaller than input

Question 24

If a bottle was filled with water and had holes at different heights, what would happen

Answer 24

The deeper the whole, the higher the pressure so the water is pushed with a greater force so has a bigger horizontal range

Question 25

Pressure =

Answer 25

Weight of liquid/area

Question 26

Pressure depends on 2 things:

Answer 26

How much force is applied
How big (or small) the area on which the force is applied

Question 27

Equation for hydraulics

Answer 27

Force A/Area A = Force B/Area B

Force B/Force A = Area B/Area A

Question 28

What does a smaller force on piston A mean (hydraulics)

Answer 28

Smaller force on piston A will produces a larger force on piston B because the pressure of the liquid is constant. This acts as a force multiplier

Question 29

What is the atmosphere

Answer 29

A relatively thin layer of air around the Earth

Question 30

The greater the altitude…

Answer 30

The less dense the atmosphere and the lower the atmospheric pressure because there is less air above the surface so there is smaller weight of air acting on the surface since p=F/A

Question 31

How is upthrust created

Answer 31

The bottom surface of an object submerged in a liquid experiences a greater pressure than the top surface, creating a resultant force called upthrust

Question 32

When do objects float

Answer 32

When its weight=upthrust
If the density is less than the fluid
When the weight of the object= weight of fluid displaced

Question 33

What is momentum

Answer 33

Any object that moves has momentum

Question 34

What is the formula for momentum

Answer 34

Momentum = mass x velocity (p=mv)

Question 35

What are the units for momentum

Answer 35

kgm/s

Question 36

Why is a ball harder to stop if it has a large mass and is moving at a high velocity

Answer 36

Because there’ll be a greater force exerted on a person’s hand and the person will have to exert an equal and opposite force on the ball to stop it, the greater the force required, the harder it’ll be to stop

Question 37

In any collision or explosion momentum is…

Answer 37

Conserved (provided there are no external forces having an effect e.g. friction or gravity)

Question 38

Force =

Answer 38

Change in momentum / time