Forces & the Electromagnetic Spectrum

Summary Notes

Name ………………………………………………………….. Class ………………………..

S2 Science

2

Gravity, Weight and Mass

The force of gravity pulls everything towards the centre of the Earth.

Another name for the force of gravity is weight. A Newton balance is used to measure force in Newtons (N). Your weight would change if you visit another planet. On a larger planet, your weight would be greater.

Mass is the amount of material in an object and is measur- -ed in kilograms (Kg). Mass stays the same even if you travel to another planet. Example : mass = 5 Kg, on Earth, weight = 5 x 10 = 50 N The gravitational field strength on earth is 10 N/Kg.

Balanced and Unbalanced Forces

Forces are balanced when they are equal in size but acting in opposite directions. When one force is bigger than the other, the forces are unbalanced. An unbalanced force can change an object’s speed. It can make it speed up or slow down. Sir Isaac Newton had a theory about gravity (and relativity).

Weight = mass x gravitational field strength

Test yourself questions A

Try answering the following questions in sentences : 1) What does the force of gravity do to all objects ? 2) What is another name for the force of gravity ? 3) How can you measure a force ? 4) What unit is force measured in ? 5) What happens to your weight if you visit … a) the Moon b) Jupiter 6) What is mass ? 7) What unit is mass measured in ? 8) What happens to your mass if you visit … a) the Moon b) Jupiter 9) What is the value of ‘g’ on Earth ? 10) If your mass is 50 Kg, calculate your weight on Earth.

(Now check your answers at the back)

5

Surface Friction Surface friction occurs when surfaces rub together. Sometimes a lot of friction is good :

Sometimes we want less friction : Surface friction can be reduced by using lubrication : oil Friction means that energy is lost as heat in all moving Systems. John Boyd Dunlop was a famous Scottish scientist who invented tyres.

water

Air Friction When an object moves through the air, it experiences an air friction force. This force is called drag. Drag can be reduced by making objects streamlined - smooth and pointed.

….. like a dolphin.

….. or a shark ...

….. or the ‘Black Bird’ high altitude spy plane.

Test yourself questions B

Try answering the following questions in sentences : 1) What causes surface friction ? 2) Write down 3 situations where there is a large amount of surface friction. 3) Write down 3 situation where you want less friction. 4) What is lubrication and give an example ? 5) What causes heat to be generated in moving systems ? 6) Who had a theory about gravity ? 7) Who invented tyres ? 8) What do we call the air friction force ? 9) Streamlining reduces drag. Explain how. 10) Write down 3 examples of streamlined objects.

(Now check your answers at the back)

Electromagnetic Spectrum The EM spectrum contains a group of radiations that carry energy and travel through the vacuum of space.

These radiations all travel at the same speed, 300 million metres/second. This is called ‘the speed of light’. Radiations and how they are useful : Two famous Scottish scientists :

John Logie Baird - invented the television. Robert Watson-Watt - invented radar.

Radiation Use

Gamma rays Kills cancer cells

X rays Detects broken bones

Ultra violet Suntan, security marking

Visible light We see colours, telescope

Infra red Thermometer, heats muscles

Micro waves Mobile phones, oven

Radio/tv waves Radio, tv, telescope.

Test yourself questions C

Try answering the following questions in sentences : 1) Write down 3 things that all electromagnetic waves have in common. 2) What is a vacuum ? 3) How fast do these radiations travel ? 4) Name two uses of ultra violet radiation. 5) Name two uses of micro waves. 6) Name two different types of telescope. 7) What is John Logie Baird famous for ? 8) Who invented radar ? 9) How many scientists that you have studied in this unit are Scottish ? 10) What theory is Sir Isaac Newton famous for ?

(Now check your answers at the back)

10

Answers to test yourself questions A : 1) Gravity force pulls everything towards the centre of the Earth. 1) Another name for the force of gravity is weight. 2) A Newton balance can be used to measure a force. 3) Force is measured in Newtons. 4) a) Weight decreases on the Moon. b) Weight increases on Jupiter. 6) Mass is the amount of material present. 7) Mass is measured in kilograms. 8) a) Mass stays the same on the Moon. b) Mass stays the same on Jupiter. 9) Weight = mass x gravitational field strength constant 10) On Earth, g = 10 N/Kg

Answers to test yourself questions B : 1) Surface friction is caused when surfaces rub together. 2) Break/tyre, road/tyre, hand/wall. 3) Ski/snow, ice skate/ice, moving parts in a car engine. 4) A substance placed between moving parts, eg oil, water 5) Friction generates heat in moving systems. 6) Sir Isaac Newton had a theory about gravity. 7) John Boyd Dunlop invented tyres. 8) The air friction force is called drag. 9) Streamlining means an object is smooth and pointed. 10) Dolphin, shark and ‘Black Bird’.

Answers to test yourself questions C : 1) Carry energy, travel through a vacuum, travel at the same speed (300 million metres/sec). 2) A vacuum is a region of space that has no air particles. 3) EM radiations travel at 300 million metres/sec. 4) Suntan, security marking. 5) Mobile phones, ovens. 6) Light/optical telescope and radio telescope. 7) John Logie-Baird invented the television. 8) Robert Watson-Watt invented radar. 9) Three scientists in this unit are Scottish. 10) Sir Isaac Newton is famous for his theory about gravity.