Topic 9 - Forces and their effects

Question 1

What are the four types of energy transfers?

Answer 1

Mechanical work, Electrical work, Heating and Radiation

Question 2

What is mechanical work?

Answer 2

A force moving an object through a distance

Question 3

What is electrical work?

Answer 3

Charges moving due to a potential difference

Question 4

What is Heating?

Answer 4

Due to temperature difference caused by electrically pr by a chemical reaction.

Question 5

What is Radiation?

Answer 5

energy transferred as a wave eg light, infrared, sound - the Sun emits light radiation and infrared radiation

Question 6

What does doing ‘work’ mean scientifically?

Answer 6

Energy being transferred

Question 7

What happens when a force moves an object through a distance?

Answer 7

Work is done and energy is transferred

Question 8

How do you work out Work done?

Answer 8

Work done (J) = Force (N) x Distance (m)

Question 9

What does a force doing work cause?

Answer 9

Rise in temperature

Question 10

How do you work out power using work done?

Answer 10

Power (W) = Work done (J) / Time taken (s)

Question 11

What are non-contact forces?

Answer 11

Forces that can be exerted on objects without touching each other. Gravity, Magnetism and Electrostatic charges are examples.

Question 12

What are Contact forces?

Answer 12

Forces that can be exerted between objects due to them being in contact. Normal contact force and the force of friction are contact forces.

Question 13

What is the difference between vector and scalar quantities?

Answer 13

A scalar quantity has magnitude but no particular direction. A vector quantity has magnitude and acts in a particular direction.
Scalar: Speed, Volume, Mass, Temperature, power, energy and time.
Vector: Force, Velocity, Acceleration, Displacement and Momentum

Question 14

What is a free-body diagram?

Answer 14

Represents all forces on a single body. Larger forces are shown with larger arrows. They need to contain: the body the forces are acting on, represented by a dot or box; and the forces acting on the body.

Question 15

What happens if the arrows are balanced on a free body diagram?

Answer 15

This means that the resultant force is zero and therefore is stationary or moving at a constant speed.

Question 16

When can a force cause an object to rotate?

Answer 16

When the force on a spanner cause a turning effect on the nut to loosen it.

Question 17

What is the turning effect of a force called?

Answer 17

Moment (Nm)

Question 18

How do you work out the moment of a force?

Answer 18

Moment (Nm) = force (N) x perpendicular distance from pivot to force (m)

Question 19

How do you create a larger moment?

Answer 19

increase the force or perpendicular distance.

Question 20

What are gears?

Answer 20

Circular cogs with ‘teeth’ around the edge. Their teeth interlock so that the turning one can cause another to turn, in the opposite direction. Interlocked gears rotate at different speeds - larger the gear, the slower it spins.

Question 21

How do to work the speeds and moments between a large gear (16 teeth) and a medium gear (8 teeth)?

Answer 21

Ratio of teeth = 16:8 = 2:1
This means that for every 1 turn the large gear does, the medium gear will do 2 turns.
The force applied to gear is the same, and the radius of a gear is equal to the distance of the applied force from the pivot. As moment = force x distance, this means that the ratio of moments of two gears is equal to the ratio of the gear’s radii, and therefore equal to the ratio of teeth. The moment of the largest gear to the medium gear is also 2:1 so the moment gets doubled.

Question 22

What does the principle of moments state for an object in equilibrium?

Answer 22

The sum of anti-clockwise moments = The sum of clockwise moments

Question 23

How do levers transmit the rotational effects of forces?

Answer 23

If you push one end of the lever down, the rotation around the picot cause the other side to rise. Levers make it easier to do work as they increase the distance from the pivot at which the force is applied, the longer the lever, the smaller the force needed to give the same moment.

Question 24

How does lubrication reduce unwanted energy transfers?

Answer 24

It reduce friction and therefore unwanted energy transfers. It improves the efficiency of machines.