Forces and Energy

Question 1

Example of energy being transferred by heating

Answer 1

• a pan of water is heated on a gas camping stove
• when the system is the pan of water, energy is transferred into the system by heating to the thermal energy stores of the pan and water, increasing their temp.
• when the system is the camping stove and the pan, energy is transferred within the system - from the chemical energy store of the gas to the thermal energy stores of the pan and water, increasing temp.

Question 2

Example of energy being transferred by forces doing work

Answer 2

• a box is lifted up off the floor; the box is a system
• as the box is lifted, work is done against gravity
• this causes energy to be transferred to the box’s kinetic and GPE stores

Question 3

Example of energy being transferred by electrical equipment

Answer 3

Electrical devices work by transferring between different energy stores….
- an electric toothbrush is a system
- it transfers energy from the chemical stores of its battery to the kinetic energy store of its bristles
- some energy is also transferred into the surroundings through by sound and by heating

Question 4

What does work done mean?

Answer 4

When a force moves an object through a distance, work is done on the object and energy is transferred

Question 5

SP8a Work and Power

Describe what is ment by;
A) Energy
B) Power

Answer 5

A) Energy is transferred whenever things happen, Energy can also be transferred when a force makes something move.
- The energy transferred by a force is called work done.
- Equation: Work done ( J ) = force ( N ) x Distance moved ( m )

B) Power is the rate at which energy is being transferred. Power is measure in watts ( W )
- 1 watt means 1 joule of work done per second.
- Equation: Power ( W ) = Work done ( J ) / time taken ( s )

Question 6

SP9a Objects affecting eachother

Describe what is ment by a;
A) Contact Force
B) Non-Contact Force
( Provide Examples )

Answer 6

A) This force is present when objects are touching eachother.
- E.X1 When you stand on the floor, there is an upward force on you called the normal contact force.
- E.X2 A boat needs an engine to keep it going due to the water resistance slowing it down, this is a form of friction.

B1) These are forces that can act on objects even while they are not in contact.
- E.X1 A boat on water is floating due to upthrust ( contact ), which is being balanced out by gravity ( non-contact ).

B2) The space around an object where it can affect other objects is called a force field.
- E.X1 Magnetism - a magnet can attract magnetic materials like iron nickle etc, the space where it can affect others is called a magnetic field.
- E.X2 Electrostatic - An object charged with static electricity has an electric field around it. 2 objects with the same charge produce a pair of forces the same size in opposite directions.

Question 7

SP9a Objects affecting eachother

Describe how gravity can affect 2 objects

Answer 7

1. Gravity is a force that occurs between any 2 objects with mass.

2. The Gravitational forces between 2 objects can be represented with as vectors ( arrows that show both direction and magnitude )

3. These 2 forces are action-reaction forces ( pairs of forces acting on different objects )

Question 8

SP9b Vector diagrams

A) What is a free body force diagram
B) Describe how you would use a scale diagram to find resultant force.
C) Describe how you would use a scale diagram to resolve forces

Answer 8

A) This a method of showing all of the forces acting on an object.

B1) Draw arrows at the correct angle to represent the forces. The length of each arrow represents the size of the force.

B2) Draw lines to make a parrellegram

B3) The resultant forces is the diagonal of the parrellogram. Measure this arrow to work out the size of the resultant force.

C1) Draw a force arrow to scale at the correct angle

C2) Draw a rectangle with the sides in the directions you are interested in ( e.g. horizontal and vertical )

C3) The resolved forces are the sides of the rectangle.

Question 9

SP9c Rotational forces

A) Define what a moment is
B) Describe factors that can affect a moment
C) Provide the formula for a moment

Answer 9

A) A turning force is called a moment

B) The moment of a force depends on the size of the force and where the force is applied.
- The greater the force, & the futher away it’s applied from the pivot, the greater the moment.
- The distance between the force & pivot is measured at normal ( right angles ).

C) Moment of a force (Nm) = force (N) x distance normal ( perpendicular ) to the direction of the force (m)

When a system involving rotational forces are in equilibrium;
- The sum of clock wise moments = sum of anti-clockwise moments

Question 10

SP9c Rotational forces

Describe how;
A) Levers
B) Gears
Transmit the rotational effect of forces

Answer 10

A) A lever is a bar that pivots about a point and is used to transfer a force, by being further away from the pivot point.

B) Gear A could be driven by a water wheel, this rotation is passed onto Gear B by the interlocking teeth, and this drives the milling stones.
- If Gear A has 8x the amount of teethe that Gear B does, then each complete turn of A completes 8 turns for B.

Question 11

SP3b Energy Effiency

Explain why machines waste energy when they get hot & how this can be prevented.

Answer 11

• Whenever 2 moving parts touch eachother, friction causes them to heat up.
• The thermal energy stored within the machines is transferred to the surroundings by heating, which dissipates the energy.
• This energy is wasted energy
• Prevention: Friction between moving parts can be reduced by lubrication. Oil or other liquids, and sometimes even gases can be used as** lubricants**