1. By: Pawitra & Raina

2. Speed
 Is a steady rate of movement over a distance.

3. 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.

4. 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.

5. 4. Light gates
 In a light gate a beam of light shines onto a light-
sensitive switch.

6. 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.

7. Velocity
 Is the speed and the direction of movement when given
together.

8. 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

9.  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.

10. 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.

11. 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.

12. 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.

13. 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.

14. 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.

15. Streamlined shapes
 Shapes that are designed to reduce air
resistance.

16. Dragster
 Is a vehicle which accelerates quickly.
Parachute
 Is used to bring sky divers safely to the ground.

17. 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.

18. Terminal velocity
The velocity at which an object falls through air when
the air resistance balances the weight of the object.

19. 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.

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

21. Upthrust
The upward force exerted on an object by the liquid
or gas around it that it displaces.

22. Unbalanced forces
 A force that together can equal a certain number
and will make a change of the objects motion.

23. 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

24. Weightlessness
 True weightlessness could only occur far out in deep space
where there are no large objects with gravitational fields.

25. 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

26. Moving the Earth
 The force producing the acceleration is a centripetal force
produced by the gravitational force between the Sun and
the Earth.

27.  It moves in an orbit around a planet.
 It causes by the gravitational force between the
planet and the moon.

28. 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.