Additional Forces Seperate science

Question 1

What is the moment of a force?

How do you calculate the moment of a force?

Answer 1

The moment of a force is the turning effect that that force has about a pivot.

To calculate the moment of a force you use this equation:

Moment = Force x perpendicular distance from pivot

Moment is measured in Newton meters (Nm)

Force is measured in Newtons (N)

distance is measured in meters (m)

Question 2

State two ways in which you can increase the moment of a force

Answer 2

Increase the size of the force

Increase the distance of the force from the pivot

Question 3

Explain what a force multiplier lever is

Give an example of a force multiplier lever

Answer 3

A force multiplier lever is a bar that is used to allow a user to lift up a heavier weight than they normally would be able to. It does this by multiplying the force by having the load closer to the pivot than the force.

Example: A wheelbarrow

Question 4

Explain how you use forces to tell if an object is rotating or not?

Example calculation:

Is this system balanced or not?

Answer 4

Calculate the clockwise and anticlockwise moments. If they are equal then the object is in balance.

The clockwise moment is 300Nm and the anticlockwise moment is 320N. This means it is not balaned, it will fall in a clockwise direction.

Question 5

Explain why the input force on a force multiplier will move further than the output force.

Answer 5

The law of conservation of energy states that:

energy transferred by a force (Work done) = Force x distance

if the force is multiplied by a certain factor, the distance moved through must be reduced to keep the total energy input equal to the total energy output, satisfying the law of conservation of energy

Question 6

What is the purpose of a gear system?

Answer 6

A gear system is used to increase or decrease the force exerted by rotational motion, such as a motor

Question 7

Explain the effect of using a large gear to drive a smaller gear when they are connected through the axel.

What would happen if the small gear drove the larger one?

Answer 7

If a larger gear drove a smaller gear then the size of the force would increase but the distance that the object moves would be reduced.

If it was the other way round the force would reduce but the distance moved would increase

This is becuase of the law of conservation of energy, where energy transferred = force x distance. As the energy stays constant the force must increase when the distance reduces

Question 8

Explain the effect of using a large gear to drive a small gear when they are tooth to tooth.

Answer 8

When they are tooth to tooth the moment that is created is reduced but the anglular velocity (the number of times it spins in one second) is increased.

Question 9

Explain how to investigate the effect that a gear system has on the force

Answer 9

1. Set up the equipment as shown in the diagram
2. Measure the diameter of each wheel and record this in the table
3. Hang a 300 gram mass from the larger wheel
4. Add masses to the smaller wheel and note the mass required to lift the 300g mass attached to the larger wheel.
5. Repeat the experiment with a range of diameters for the smaller wheel.
6. Compare the ratio of the diameters to the ratio of the masses.

Question 10

For this gear system, the driving wheel with 10 teeth has an angular velocity of 9 radians/second. What is the moment of the output cog?

Answer 10

3 Radians per second

There are 3x as many teeth, and as they interlock one rotation of the smaller cog is 1/3 of a rotation of the larger cog, this means it will rotate at 1/3 of the speed.

Question 11

Explain why the two gear experiment (shown in the diagram) may overestimate the force required to move the mass attached to the other wheel.

Answer 11

There is friction acting between the pivot and the axel, the force of the masses connected to the smaller wheel needs to create a moment that is great enough to overcome both the moment of the masses of the larger wheel and the moment of the friction in the pivot.

Question 12

If a gear of radius 10cm is used to drive a gear of radius 40cm which is connected through the axel, with a driving force of 8 N, what is the size of the force exerted by the driven gear?

Answer 12

The moments driving the first gear:

Moments = force x perpendicular distance from pivot

8 x 0.1 = 0.8 Nm

This is the same moment that is experienced by the second gear, but this has a radius of 0.4 m. Therefore using moments equation

Force = moments/distance

= 0.8/0.4 = 2N

Question 13

What is the principle of moments?

Answer 13

When something is in equilibrium (it is balanced) the sum of the clockwise moments is equal to the sum of the anticlockwise moments

Question 14

If a 50g mass is placed 30cm from the pivot, how far away would a 20g mass need to be in order to balance it.

Answer 14

1. find the weight of each of th emasses using the formula W = mg. As g on earth is always 10:

50g mass:

mass = 0.05kg

weight = 10 x 0.05 = 0.5N

Using the same logic the mass of the 20g mass is 0.2 N

2. find the moments of the 50g mass:

moments = force x perpendicular distance from pivot

= 0.5 x 0.3m = 0.15Nm

3. This is the same as the moments of the 20g mass therefore:

distance = moments/force

= 0.15/0.2

= 0.75m

Question 15

Calculate if this beam will balance or not