Forces

1) What is a Force ?
They are usually pushes or pulls. (they can also be twists)
A force always acts in a certain direction.
Forces normally occur between two objects that are touching (or in contact)
However some forces can occur without contact.

2) Forces can be used to make objects do 7 things, what are they ?
make an object start moving / constant speed
make an object stop moving
speed up / accelerate
slow down / decelerate
change direction
turn/pivot/twist
change shape/deform

3) Can you give some example of Contact Forces ?
Friction, Upthrust

4) Can you give some examples of Non-Contact Forces ?
Gravity - (gravitational force) everything falls to the floor
Magnet - (magnetic force) magnets will attract paper clips towards it
Static Electricity - (electric force) electric charge that is not flowing (static charge on a balloon)

A field is a region where an object experiences a non-contact force.

5) What is aerodynamic lift ?

6) How are forces measured, what is the unit ?
Newtons (N)

7) What is the difference between balanced and unbalanced forces ?
Balanced forces - are equal in size but opposite in direction. The net force is zero. Objects can be stationary or moving at a constant velocity. Also called a Reaction force.
Unbalanced forces - are not equal in size or not in the same direction.

8) What is Friction ?
Friction is a contact force that always acts in the opposite direction to the movement.
For an object to move the force must be larger than the friction (or resisting force).
Friction only occurs when an object is moving and two surfaces rub together.
When an object tries to pass through a gas or liquid there will be some friction/resistance.
The rougher the surface, the more friction there is.

9) What is Air Resistance ?
This is a frictional force that pushes against the object trying to move through the air, also referred to as drag.
The faster the object moves the greater the resistance.
When the frictional force equals the opposing force the object moves at a steady speed.
The fastest car on land travelled at 763 mph.

10) What is Water Resistance ?
This is a frictional force that slows objects down when they pass through water, also referred to as drag.
The fastest boat on water travelled 316 mph.
The fastest submarine travelled at 51 mph (44 knots).

11) What is Weight ?
The force acting on an object because of gravity.
Often referred to as Mass.

12) What is Density ?
This is how heavy a material is for its size.
This is a measure of how many particles there are in a given space.
Density is the amount of mass in a given volume. How closely packed they are.

13) What is the formula that connects density, mass and volume ?
density = mass / volume

14) Can you describe the density in solids, liquids and gases ?
Solids usually have a higher density than liquids.
Liquids usually have a higher density than gases.
When a solid is heated, the particles move around more and move further apart
The substance expands and becomes less dense.
Solid to Liquid, density decreases, volume increases
Liquid to Solid, density increases, volume decreases.

15) When H2O changes from a liquid to a solid, does the density increase ?
No. H2O is the only known non-metallic substance that actually expands when it changes from liquid to solid.
Its density actually decreases and it expands approximately by 9% volume.

16) When ice melts, does its volume increase or decrease ?
This is solid to liquid, density decreases, volume increases.

17) Why do icebergs float ?
The density of ice is lower than the density of water.

18) What is the opposite of Expand ?
Contract.

19) What is a Force Diagram ?
It is a drawing with arrows to show all the forces acting on an object.

20) What is Upthrust ?
This is a contact force that pushes things upwards.
In liquids the pressure increases with depth due to the weight of the water above it.
Liquid pressure causes upthrust and makes things float.

21) What are the units of Pressure ?
Pascals, Pa (N/m2)

22) When does an object sink ?
If the object is denser than the liquid, the object will sink.
Salty water is denser than pure water, which makes it easier for objects to float.

23) How can a large ship float ?
There is a lot of air inside the ship which means that it is not as dense as water.
If the upthrust is equal to the objects weight, the object will float.
The force pushing upwards at the bottom of the object is greater than the force pushing down at the top of the object.

24) Why do helium balloons float in air ?
Anything that is less dense than air will float, although air is not very dense.

25) When is there a change in speed or direction ?
There is a change in speed or direction when the forces are unbalanced

26) When forces make an object turn, what is the Moment ?
The moment is the name given to the force that is creating the turning effect
When a force acts on something that has a pivot, it creates a moment (or turning effect)
Moment = Force x Distance

27) What are Levers, Pulleys and Gears ?
A lever uses force on a pivot to lift the load.
A pulley uses a flexible cable across a wheel to lift the load.
A gear uses wheels with teeth to transfer motion and power from one to another.

28) What is Tension ?
State of being stretched tightly.

29) How can you Deform an object ?
You can use forces to stretch or compress objects
When an object deforms it changes its shape
A spring is an example of an object that can compress

30) What is Hooke's law ?
This only applies to Springs.
This says the amount it stretches (the extension) is directly proportional to the force applied (the weight).
For springs, the force at which Hooke's law stops working is much higher than for most materials, springs are unusual.
F = ke

31) What is Compression ?
A force that is squashing or pushing that changes the shape of an object

32) How does an Insulator effect the rate of energy transfer ?
Some materials transfer energy faster than others.
Materials that transfer energy slowly (using conduction) are called insulators.
Insulators help to keep hot objects hot and cold objects cold.

33) What are the different Energy Resources ?
Most of our energy originates from the sun.
Fossil Fuels (non-renewable) - Sun - Light - Photosynthesis - Dead Plants/Animals - Fossil Fuels
Biomass - Sun - Light - Plants - Photosynthesis - Biomass
Wind - Sun - Light - Heats atmosphere - Air Moves - Wind
Wave - Sun - Light - Heats atmosphere - Air Moves - Wind - Waves
Solar - Sun - Light - Solar Cells - Electricity

34) Describe how electricity can be generated from fossil fuels ?
Fuel is burnt and water is turned into steam. Energy is transferred from Chemical to Thermal.
The thermal energy is then transferred to Kinetic energy used to drive a Turbine which generates the electricity.
The kinetic energy is then transferred into electricity.

35) What does the power rating of an electrical appliance tell you ?
This tells you how fast the energy will be transferred.

36) What is Power and how is it measured ?
Electric power is the rate of transfer of electrical energy within a circuit.
Power is usually measured in watts (W) or kilowatts (kW).

37) What will transfer more energy, a 200W device left on for an hour or a 300W device left on for an hour.
The 300W because it has a higher power rating.

38) Two identical cranes can transfer 20 KJ of energy to lift an object. Which crane can lift the object the highest ?
One crane applies a big force and the other crane applies a small force.
A large force can be applied over a small distance.
A small force can be applied over a large distance.

39) What is Speed ?
Speed is a measure of how far you travel in a given amount of time.
Speed is Distance over Time.

40) What is Velocity ?
Velocity is speed in a particular direction.

41) What are the 3 common units of speed ?
metres per second (m/s), miles per hour (mph), kilometres per hour (km/h).

42) What does the gradient show on a Distance-Time Graph ?
The gradient on a distance-time graph is the speed of the object.
The steeper the line, the faster the object is moving.

43) What does a straight line show on a distance-time graph ?
A straight line represents a constant speed.