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Motion of vehicles- stopping distance = thinking distance + braking distance
The meaning of Thinking and Breaking distance.

thinking distance- is the distance a vehicle travels in the time it takes for the driver to apply the brakes after realising they need to stop. braking distance- is the distance a vehicle travels in the time after the driver has applied the brake.

Changes in energy-

There are eight main stores of energy:

1. magnetic

2. internal (thermal)

3. chemical

4. kinetic

5. electrostatic

6. elastic potential

7. gravitational potential

8. nuclear

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According to Newton's first law of motion, an object remains in the same state of motion unless a resultant force acts on it. If the resultant force on an object is zero, this means:

a stationary object stays stationary

a moving object continues to move at the same

velocity

(at the same speed and in the same direction)

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An ion is an atom or group of atoms with a positive or negative charge. Ions form when atoms lose or gain electrons to obtain a full outer shell:

metal

atoms lose electrons to form positively charged ions

non-metal

atoms gain electrons to form negatively charged ions

Forming positive ions

Metal atoms lose electrons from their outer shell when they form ions:

the ions formed are positive, with more

protons

than electrons

the ions formed have full outer shells

For elements in groups 1, 2 and 3, the number of electrons lost is the same as the group number.

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Some elements have properties that are not typical. For example:

mercury (a metal) has a low

melting point

and exists as a liquid at room temperature

graphite, a form of carbon (a non-metal), has a high

boiling point

and is also a good

conductor

of electricity

A substance with a high density means it has a high mass for its size.

Malleable substances can be bent or hammered into shape without shattering, while brittle substances shatter when bent or hit.

Ductile means that a substance can be drawn out into a long wire without snapping or breaking.

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Each element is represented by its own chemical symbol. A chemical symbol:

consists of one or two letters

always starts with a capital letter, with any other letter in lower case

For example, the element mercury is shown as Hg. Do not show it as HG, hg or hG.

The periodic table shows the names and symbols of the elements. Elements are arranged into groups that share similar characteristics. Groups are numbered from 1 to 7, then 0. Metals are found on the left and non-metals are found on the right.

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Hazards

A hazard is something that could cause:

harm to someone

damage to something

adverse health effects, either straightaway or later

For example, concentrated acids are corrosive. This is a hazard because acids can damage skin and clothes if they are spilt.

Using hazard symbols

Hazard symbols are used on containers. They are there to:

indicate the dangers associated with the substance inside

give information about how to work safely with the substance in the laboratory

Hazard symbols are designed to provide a warning, even if a person cannot understand the writing that goes with them.

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Developing models of atoms

Dalton's model

John Dalton published his ideas about atoms in 1803. He thought that all matter was made of tiny particles called atoms, which he imagined as tiny solid balls. Dalton's model included these ideas:

atoms cannot be broken down into anything simpler

the atoms of a given

element

are identical to each other

the atoms of different elements are different from one another

during chemical reactions atoms rearrange to make different substances

The Dalton model has changed over time because of the discovery of subatomic particles.