By: Pawitra & Raina

Speed Is a steady rate of movement over a distance.

Ways of measuring speed

There are many ways how to measure speed:

1. The speedometer

The speedometer in a car is connected by a cable to a shaft

which turns the wheels.

2. The speed trap gun

Is a radar gun.

When the gun is fired at an approaching vehicle a beam of radio waves travels to it through the air.

3. The stop watch

Is a handheld timepiece designed to measure the amount of

time elapsed from a particular time when activated to when

the piece is deactivated.

4. Light gates

In a light gate a beam of light shines onto a light-sensitive switch.

5. Distance/time graph

The distance travelled by an object over a period of

time can be plotted on a graph called a distance/time

graph.

It can be used to study the speed of an object over

different time periods of its journey.

Velocity

Is the speed and the direction of movement when given together.

ACCELERATION

The acceleration of a moving object is a measure of how

its velocity changes in a certain interval of time.

Acceleration = change in velocity

time

SI unit for acceleration: - metres per second per second

- metres per second squared

Occurs between 2 objects when there is a pull or a

push on one of the objects which could make it move

over the surface of the other objects.

It acts to oppose a movement.

Static friction

Is the friction which exists between the 2 objects when

there is no movement.

Sliding friction

Is the frictional force between the 2 surfaces, acting on

each surface in the opposite direction to the direction of

its movement.

A closer look at friction

The surfaces of objects in contact are not completely smooth.

If we see it under a microscope, it can be seen that they have tiny projections.

Reducing friction

If a liquid is placed between the 2 surfaces the

projections are forced apart a little and the

number of connections is reduced, which in turn

reduces the force of friction.

Increasing friction

The friction between 2 surfaces can be

increased by pressing the surfaces together

more strongly.

Thinking distance A driver in a moving car sees a hazard in a certain distance

before the driver reacts and applies the brakes.

Braking distance Is the distance covered by the car after the brakes are

applied and before the car stops.

Total stopping distance Is the thinking and braking distance that will bring a car

with good brakes.

Other forces affecting speed

When objects move along a surface, friction occurs and opposes the motion.

Other forces that affect speed are:

1. Air resistance

The backward push of the air on an object moving through it.

Streamlined shapes

Shapes that are designed to reduce air resistance.

Dragster

Is a vehicle which accelerates quickly.

Parachute

Is used to bring sky divers safely to the ground.

2. Water resistance

The backward push of the water on an object moving

through it.

Barracuda can move quickly through water than a

sunfish, because they have streamlined shape on their

bodies.

Terminal velocity The velocity at which an object falls through air when

the air resistance balances the weight of the object.

Action and reaction

A force exerted by 1 object on another is always

accompanied by a force equal to it acting in the

opposite direction.

It is similar to action-reaction, but it acts on one object only.

Balanced force

UpthrustThe upward force exerted on an object by the liquid

or gas around it that it displaces.

Unbalanced forces

A force that together can equal a certain number

and will make a change of the objects motion.

Mass and weight

Mass is the amount of matter in an object.

Weight is the pull of the Earth’s gravity on the object.

Gravitational field strength = weight

mass

Earth’s gravitational field strength is 1 kg = 10 N

Weightlessness

True weightlessness could only occur far out in deep space

where there are no large objects with gravitational fields.

Planet Gravitational field strength

Mercury 0.38

Venus 0.9

Earth 1

Mars 0.30

Jupiter 2.64

Saturn 0.925

Uranus 0.79

Neptune 1.12

Pluto 0.05

Moving the Earth

The force producing the acceleration is a centripetal force

produced by the gravitational force between the Sun and

the Earth.

It moves in an orbit around a planet.

It causes by the gravitational force between the

planet and the moon.

Definitions

Centripetal force = the forces that acts on an object moving in a circle, pulling it in towards the centre of the circle.

Streamlined shape = a shape that allows an object to move easily through air or water.