Forces Flashcards
1
Q
What is a force?
A
A force is a push or pull on an object.
2
Q
What do forces change?
A
Forces can change the shape, the speed, and the direction of an object.
3
Q
What is force measured in?
A
Force is measured in units called Newtons.
4
Q
How can the size of a pulling force be measured?
A
The size of a pulling force can be measured using an instrument called a newton balance.
They are sometimes called spring balances.
5
Q
How do you measure a force using a newton balance?
A
When you pull gently on the hook of a newton balance, the pointer moves down depending on the force.
6
Q
Why do different newton balances have different springs and scales?
A
Some springs can be tighter/slacker which allows a variety of different sizes of forces to be measured.
7
Q
What causes the spring to stretch when the object is hanging from it?
A
The pull of gravity
8
Q
What type of force does earth exert on all objects and why?
A
The earth exerts a pulling force on all objects. The force is due to the Earths gravity.
9
Q
Where all objects of the earth being pulled towards?
A
The centre of the earth.
10
Q
What is weight?
A
Weight is the force of gravity acting on an object
11
Q
What is weight measured in?
A
Weight is measured in units called Newtons (N)
12
Q
What instrument is weight measured in?
A
Newton balance
13
Q
What is mass?
A
Mass is a measure of the amount of matter in an object.
14
Q
What is mass measured in?
A
Mass is measured in units called kilograms (kg)
15
Q
What instrument is mass measured in?
A
An electronic balance
16
Q
Is the weight of an object the same for all objects and why?
A
No because more force is needed to lift some objects up.
17
Q
How do you measure the weight of an object?
A
Hang it from the bottom of the balance, hold it steady and read the scale
18
Q
The bigger the mass…?
A
The bigger the weight
19
Q
How is the weight of an obejct calculated?
A
The weight of an object is calculated by multiplying its mass in kilograms by 10
20
Q
What do all objects with mass exert?
A
All objects with mass exert a force of gravity.
21
Q
The bigger the mass…?
A
The bigger the force of gravity.
22
Q
Why is the force of gravity exerted by the earth very large?
A
The force of gravity exerted by the earth id very large because it has a very big mass.
23
Q
Why is the force of gravity acting on an object on the moon smaller than that of earth?
A
The mass of the moon is smaller than that of earth. Therefore, the force of gravity on an object on the moon would be smaller than it would be on earth.
24
Q
What is the earth’s gravitational field?
A
The earths gravitational field is the region around the earth in which a mass can experience a force due to the pull of the earths gravity
25
What is the ratio of weight to mass called?
The ratio of weight to mass is called the gravitational field strength. It is given the symbol ‘g’ and has units of newtons per kilogram (N/kg)
26
Does the mass of an object change?
The mass of an object ( the amount of matter in the object) always stays the same.
27
Can the weight of an object change?
The weight of an object can change if it moved to a different planet or the moon.
28
What is the weight formula?
```
Weight = mass x gravitational field strength
W = mg
```
29
What is weight? (2)
Weight is a force and is the Earths pull on an object.
30
On earth, what value does ‘g’ have?
On earth, g, has an approximate value of 10 N/kg
31
What does the spring inside a newton balance do?
A newton balance has a spring inside of it. The spring extends when pulled - the extension of the spring cam give us the size of the pulling force.
32
If the extension of the spring doubles…?
The force doubles
33
If quantities A and B are said to be directly proportional, what would a graph of B against A look like?
A graph of B against A would be a straight line through the origin.
34
What is Hooke’s law
‘The extension of a spring is directly proportional to the applied force’ (only up to the elastic limit)
35
What is the elastic limit?
The elastic limit is the maximum force that can be applied to a spring, such that it will return to its original length once the force is removed. Beyond the elastic limit, the spring is permanently deformed and no longer obeys Hooke’s law.
36
When was magnetism first discovered?
Magnetism was first discovered thousands of years ago when it was found that certain types of rock attracted iron
37
What is attracted to a magnet?
A magnetic material is attracted to a magnet
38
All magnetic material…?
All magnetic material is metal but not all metals are magnetic
39
What does NCIS stand for?
Nickel
Cobalt
Iron
Steel
40
What elements do magnets attract?
Magnets attract the elements, cobalt, nickel and iron and certain materials containing any of these elements. Of these the most common are iron and its alloy, steel
41
What is an alloy?
An alloy is a mixture of two or more elements. To make an alloy, metallic elements are heated until they melt and then mixed and allowed to cool back to a solid metal. Examples of alloys are brass (a mixture of copper and zinc) and bronze (a mixture of copper and tin).
42
What is a compound?
A compound is formed when two or more elements chemically react with each other. An example of a compound is common salt (a compound of sodium and chlorine).
43
Are alloys or compounds of iron attracted to a magnet?
```
Mild steel (an alloy of iron and other elements) is attracted to a magnet.
Iron sulphate (a compound of iron and other elements) is not attracted to a magnet.
```
44
Are alloys of iron attracted to a magnet?
Alloys of iron will usually be attracted to a magnet but compounds of iron will usually not be attracted to a magnet.
45
What is a bar magnet?
A bar magnet is a rectangular shaped magnet that has a magnetic pole at each end.
46
What are the types of magnetic poles?
There are two types of magnetic poles: north pole (N) and south pole (S).
47
How can you tell which magnetic pole is north?
The north pole of a magnet is usually either coloured red or has an identification mark
48
What poles attract and repel?
Like poles repel and unlike poles attract.
49
What is a magnetic field?
The region around a magnet where it has magnetic effect is called the magnetic field.
50
What happens when a magnetic material is placed in a magnetic field?
When a magnetic material is placed in a magnetic field, it will experience a force.
51
What do iron fillings feel and show?
Iron fillings feel and effect of the magnetic field and will line up to show the pattern of the magnetic field.
52
What are the plotting compasses used to show?
Plotting compasses can be used to show the direction of the magnetic field lines.
53
Magnetic field lines?
Magnetic field lines around permanent magnets:
- are directed from the north pole to the south pole
- start and finish on a magnetic pole
54
How can the strength of a magnetic field be given?
The strength of a magnetic field can be given by the spacing of the magnetic field lines, the closed the magnetic field lines, the stronger the magnetic field.
55
If a bar magnet is hung up such that it is free to rotate, what happens?
If a bar magnet is hung up such that it is free to rotate, it lines up north/south and the same end will always points north.
56
What is the pole that points north and the pole that points south called?
The end that points north is called the ‘north seeking pole’ and the end that points south is called the ‘south seeking pole’. These names are usually just shortened to north pole and south pole.
57
What does the earth act as?
The earth acts as if it had a huge bar magnet embedded at its centre. It doesnt really, but all the nickel and iron in its core create this effect.
58
What does it mean if the north pole of a magnet points north?
Since the north pole of a magnet points geographically north, there must be a magnetic south pole at the geographic north pole.
59
Where is the earths magnetic field strongest and weakest?
The Earth’s magnetic field is strongest at tye poles and weakest near the equator.
60
What direction are field lines drawn in?
Field lines are drawn in the direction in which the north pole of a magnet (arrowhead of compass needle) points. So the earths magnetic field lines emerge from the geographic south pole and re-enter it at the geographic north pole.
61
Who discovered electromagnetism and how?
The Danish physicist, Hans Christian Oersted, first discovered electromagnetism in 1812. He held a compass near a wire which had a current flowing through it.
62
What happens when electrical charges flow in a wire?
When electrical charges flow through a wire, a magnetic field is formed around the wire.
63
What do the magnetic field lines form around a wire?
Magnetic field lines form a circle around the wire.
64
What happens when the current stops flowing?
When the current stops flowing, the magnetic field disappears.
65
How can you increase the strength of a magnetic field?
The strength of the magnetic field can be increased by coiling the wire to form a coil. This is sometimes called a solenoid.
66
What is the direction of magnetic field?
The direction of a magnetic field at a point is defined as the direction of the force on a north pole at that point.
67
Does the type of core in an electromagnet affect the strength of its magnetic field?
Yes, the type of core in an electromagnet affects the strength of its magnetic field.
68
What are some factors that can affect the strength of a an electromagnet?
Factors that might affect the strength of an electromagnet are:
- the number of loops (or turns/coils) of wire
- the current (or voltage) provided by the battery or power supply.
69
Suggest how you could measure the strength of an electromagnet?
By measuring how much mass/weight it can pick up.
70
A strong electromagnet is produced if?
- a soft iron core is placed inside the coil;
- the coil is made of a large number of turns of wire;
- a large electrical current flows through the coil
71
What are some examples of applications of electromagnetism?
Electrical bell
Relay
Loudspeaker
Recycling
72
Why are large electromagnets used for recycling?
A large electromagnet is used on a recycling plant conveyor belt to pick up and move metal cans.
73
Which metals would the electromagnet attract?
Nickel, cobalt, iron and steel
74
What advantages does an electromagnet have over a permanent magnet?
Electromagnets can be switched off
75
What is friction?
Friction is the force produced when surfaces rub together or try sliding over each other. No surface examined with a powerful microscope appears perfectly smooth. When surfaces slide over each other, tiny high points will ‘catch’ onto the other surface - this causes friction.
76
How will the force of friction affect the motion of the block?
It will decrease the speed
77
What do you think would happen to the size of the friction force between the block and the table if a weight were placed on top of the block before it was slid across the table?
The size of the friction force would increase.
78
What other factors might affect the size of the friction force between the block and the table?
Type of surface, surface area and speed etc.
79
How do frictional forces occur around a high speed boat?
Frictional forces occur due to the flow of water around a high speed boat.
80
How do fictional forces occur around a parachutist?
Frictional forces occur due to the flow of air around a parachutist.
81
What is air resistance?
The movement of air over any surface causes friction. Air friction is usually called air resistance
82
What happens to the speed of the aeroplane when the parachute is open and why?
The speed decreases because the air resistance force is large and causes the plane to slow down quickly.
83
What type of force is friction?
Friction is a force that always opposes relative motion.
Or
The force of friction opposes the motion of the body.
84
How is friction used in the braking system of a bicycle?
In the braking system of a bicycle, one surface (rubber) rubs against another (metal).
The greater the force with which the two surfaces are pushed together, the greater the friction.
85
Why do you need friction between your shoes and the ground?
There needs to be lots of friction between your shoes and the ground.
Without friction, you would not be able to push yourself foward.
86
What happens to the size of the friction force when it is icy?
It decreases.
87
What is the purpose of the tread on a car tyre?
To channel away the water and increase the friction with the road.
88
What is streamlining?
The design process to see how smoothly the air flows over the surface of the car is called streamlining.
89
What is aerodynamics?
Aerodynamics is the branch of science that deals with the motion of air and with the forces that act on objects when they move through air.
