SP8 and 9

Question 1

What is the law of conservation of energy

Answer 1

Energy cannot be created or destroyed but can only be transferred.

Question 2

What happens to make an energy change

Answer 2

A system changes causing energy to change form

I.e A motor changes electrical energy to kinetic energy

Question 3

What is a closed system?

Answer 3

It is a system which experiences no external forces

An example is a circuit which only experiences a set amount of forces.

Question 4

What happens during energy transfer in a closed system

Answer 4

In a closed system when there is an energy transfer there is no change to the total amount of energy that was within the system

Question 5

What is work done

Answer 5

It is when an external force transfers energy to a system
(Energy transferred by a force)
E.g a man pushing a boulder up a hill

Question 6

What are examples of energy change

Answer 6

A battery: The chemical potential energy within a battery will form into electrical energy

Heating: Electrical energy transfers to thermal energy, as work is done against the coils causing it to heat up

Work done: Work done is the method of energy change and transfer

Question 7

How is energy wasted

Answer 7

Energy is rarely used up 100% and so some will dissipate into the area to be stored in less useful ways

Question 8

Examples of energy waste

Answer 8

Mechanical processes waste energy in the form of heat due to friction.

The energy causes a rise in temperature as heat is lost to the surroundings

Question 9

What is power

Answer 9

Power is the rate at which energy is transferred
It is measured in watts and 1 watt = 1 joule per second

Question 10

What is efficiency

Answer 10

Efficiency is the measure of how much energy is not lost as waste

Question 11

What are examples of non-contact forces and how do they work

Answer 11

Gravity - There is a force of attraction between two objects with mass, whichever object has greater mass has a greater gravitational force

Electrostatic forces - Greater the charge the greater the force

Magnetic force - Stronger magnetic field means stronger magnetic force

Question 12

What are examples of contact forces

Answer 12

Normal contact force - The force is perpendicular to the plane of contact

Friction - When something moves across a rough surface then it experiences friction

Question 13

What is a vector and scalar

Answer 13

Vector - A force that has size and direction e.g acceleration, velocity, weight, force and displacement

Scalar - Only has magnitude e.g speed, mass and distance

Question 14

What is a free body diagram

Answer 14

It is a diagram that shows the direction of forces

Question 15

What are some key ideas of free body diagrams

Answer 15

• The reaction force only acts at the normal to the line of contact from the point of contact (It forms a right angled triangle)
• Friction acts in the opposite of any movement along the line of contact (often the ground)
• Weight always acts downward from the centre of the object’s mass

Question 16

What is a scale drawing

Answer 16

The lengths of arrows are indicative of the size of the force and can be used to work out resultant force

When two arrows are opposite but equal it means that the object has reached a state of equilibrium and have attained terminal velocity and is at a constant velocity

Question 17

What is an example of a scale diagram (Potential 6 marker)

Answer 17

6 marker - Two forces that act on a skydiver while falling are weight and air resistance
Initially skydiver only has weight but over time he accelerates causing him to have air resistance
Eventually the two forces become equal and he no longer accelerates and is instead at terminal velocity and is moving at a constant velocity

Question 18

What are the conditions for rotation to occur?

Answer 18

-If an object is attached to a pivot point (it is a point that it can rotate around but is unable to move)
-If the object has force applied at a perpendicular angle then it will rotate
-If the force is not applied not perpendicular to the object then you must find the the perpendicular from pivot to the line of a force

Question 19

What are the conditions of equilibrium

Answer 19

Equilibrium occurs when the sum of anti clockwise moments = sum of clockwise moments

Question 20

What can a gear do

Answer 20

A gear can change speed, force or direction by rotation

Question 21

What happens to a gear when it has fewer of teeth

Answer 21

What happens to a gear when it is connected to another and it has fewer teeth:
The second gear will turn faster
It will have less force
In opposite direction direction to first gear

Question 22

What happens to a gear when it has more teeth

Answer 22

What happens to a gear when it is connected to another and it has more teeth:
Turns slower
More force
In opposite direction

Question 23

Rules of gears

Answer 23

The second gear will always turn in the opposite direction
One gear will supply power
To increase power a large gear is used as a secondary

Question 24

What is lubrication

Answer 24

Lubrication reduces friction so reduces unwanted energy loss form heat and friction and increases efficiency