Exploring Contact and Non - Contact Forces

Question 1

Magnetic Fields

Answer 1

A magnetic field is a space around the magnet where a magnetic material feels a force
In a magnetic field magnetic materials such as iron can be attracted.
Other magnets can be attracted if opposite poles are close enough and repel if like poles are close enough

Question 2

Magnetic Fields 2

Answer 2

• Sprinkling the iron filings around a magnet shows the magnetic field
• The arrangement of filings shows the magnetic field lines
• The closer the lines of magnetic force are to each other, the higher the strength of the magnetic field

Question 3

Earth’s Magnetic Field

Answer 3

The Earth’s core contains materials that are rich in iron. The two well known effects of the Earth’s magnetic field are:
* Magnets line up in the N to S direction, if they are free to turn. This is how a compass works
* The Northern Lights are charged particles entering the Earth’s atmosphere they are attracted to the magnetic poles . As they collide with the gas particles in the atmosphere an amazing natural light display is created

Question 4

Earth’s Magnetic Field 2

Answer 4

• The Earth also has a gravitational field, which is the region around the Earth where the force of gravity acts
• The gravitational field attracts all masses, whereas only particular materials are affected by the magnetic field

Question 5

Exploring Gravity on Earth

Answer 5

• Gravity is a pulling force that exists between all objects.
• For small objects the force is tiny and unnoticable, but when one of the objects is a planet, gravity is certainly a force to be reckoned with.
• The gravitational field of Earth reaches well into space

Question 6

Gravity and Weight

Answer 6

• The stronger gravity is, the greater the weight of an object
• The strength of the Earth’s gravity gets weaker the further from Earth you move away

Question 7

Gravity - Space Stations

Answer 7

• In space stations that are orbiting around the Earth, astronauts look as if they have no weight. However, Earth’s gravity is attracting them and also the space station at the same rate

Question 8

The Earth’s Gravitational Field

Answer 8

• The region around the Earth affected by it’s gravity is its gravitational field
• The field can be represented by straight lines of force. Where the lines are close together, the field is stronger. If the lines are further apart the weaker the field
• Gravity doesn’t stop at Earth’s surface. In addition the gravity continues towards the middle of the Earth

Question 9

Acceleration Caused by Gravity

Answer 9

• Acceleration is a change in the speed or direction of an object’s movement.
• Within the Earth’s gravitational field unsupported objects accelerate towards the Earth unless it is prevented by other forces

Question 10

Acceleration caused by Gravity- 2

Answer 10

• Think about someone dropping an object. It starts to fall and gets faster
• By the end of the first second it is falling it 10 m/s
• During the next second the object continues to accelerate and by the end of that second it is falling at 20m/s
• For every second of freefall the speed increases by 10m/s. We say that the acceleration due to gravity is 10m/s^2

Question 11

Spreading the Force

Answer 11

When the force of weight is spread over a large area this reduces the pressure on the object. Example : A camel spreading its feet across the sand to stop itself from sinking
If the force of weight is acting over a small area the pressure is greater. Example: A knife used to cut vegetables concentrates a force over a very small area

Question 12

Calculating Pressure

Answer 12

**Pressure = Force/Area
The force is measured in newtons (N) and the area is measured in square meters, so the pressure is measured in newtons per square meter (N/m^2)
The unit for pressure is pascals (Pa)
1 Pa = 1N/m^2

Question 13

Important Formulae

Answer 13

**P = F/A (N/m^2 or Pa)
F = A*P (N)
A = F/P (m^2)

Question 14

How Pressure Varies

Answer 14

• When we are on land the pressure inside our body is the same as the pressure of the air around us. However, when people go diving, there is extra pressure from the water above.
• The greater the depth the higher the pressure
• In deep water the pressure will be the same all over your body

Question 15

Density

Answer 15

• Density is the amount of mass in the particular volume of a material.
• If a material is denser than water it will sink
• If the object is less denser than water it will float

Question 16

Buoyancy and Upthrust

Answer 16

• When an object is in water, the water provides a buoyancy force called upthrust
• If the force of weight is bigger than the upthrust then the object will sink.
• Even when it sinks it is partially supported by upthrust.
• When an object floats, its entire weight is supported by upthrust

Question 17

Measuring Upthrust

Answer 17

• The weight of an object can be compared with it’s weight in water. The difference between the two is the difference in upthrust provided by each.
• Water is displaced when an object is lowered into it. The weight of the displaced water is the same as the size of the upthrust force.
• The size of the upthrust force depends entirely on the volume of water displaced
• Neutral buoyancy happens when an object neither sinks to the bottom nor bobs up to the surface. It appears to hover

Question 18

Exploring Gas Pressure

Answer 18

• The pressure of the atmosphere varies with height.
• High up the mountains. the atmospheric pressure is much lower than at sea level
• In space there is no atmosphere so there is no pressure

Question 19

Explaining Pressure in the atmosphere

Answer 19

• The atmosphere contains molecules of oxygen, nitrogen and carbon dioxide as well as of other gases
• The force of gravity pulls all these particles towards the Earth. This causes the atmosphere to press down on the Earth and everything on it
• This process is called atmospheric pressure
• The particles in the air are constantly moving on the Earth’s surface and they lie in a compact layer. The higher you go from the Earth’s surface, the more space there is between the particles

Question 20

Pressure and Weather

Answer 20

• The atmospheric pressure is continually changing accross the world.
• Where there is high pressure, the weather tends to be dry and sunny because the higher downward force of the atmosphere reduces the cloud growth
• Where there is low pressure, clouds can develop more easily and it is more likely to rain.

Question 21

Presure and Weather 2

Answer 21

• The lines in a weather chart are called isobars.
• Isobars link areas of equal pressure.
• Where there are big pressure differences accross the region, the isobars are closely packed together and the winds will be strong

Question 22

Weather Fronts

Answer 22

• Weather fronts are where warm and cold air masses collide. Lots of cloud usually form at weather fronts
• The weather fronts are marked on the chart as lines with triangular and semi - circular shapes along their length

Question 23

Working With Pressure

Answer 23

• A life support machine gently increases air pressure so that the air fills the lungs of a patient who is having difficulty breathing
• The machine then reduces the pressure so that the air leaves the lungs.

Question 24

Dealing With Low Air Pressure

Answer 24

• Passenger jets fly at around 10,000m above sea level where th atmospheric pressure is low and oxygen is scarce.
• The cabin is pressurised as the aircraft climbs so that even when fly over 10,000m the cabin pressure is equivalent to being at around 2,000m
• In case, there is a fault in aircraft systems, all commercial airlines are fitted with oxygen masks that supply oxygen from the backup system.

Question 25

Measuring Pressure

Answer 25

• The historical methosd for measuring pressure uses a barometer
• This instrument contains a sealed flexible container of air that expands as the atmospheric pressure decreases and contracts as the pressure increases
• The flexible contsainer is linked to a pointer that moves over a scale

Question 26

Measuring Pressure 2

Answer 26

• Modern pressure sensors and digital displays have taken over and are small enough to build into a wristwatch
• One complication for altimeters is that atmospheric pressure varies from day to day and place to place.

Question 27

Pressure and Movement

Answer 27

• The pressure of the air in a bicycle tyre is a lot higher than that of the air in the atmosphere. This is achieved by using a pump that compresses air inside
• The pump is attached to the tryre via a valve which lets air move from the pump into the tryre but not the other way
• When the pressure is higher in thepump than in the tyre the air moves throught the valve into the tyre.