The_Nature_of_Forces grafe 8 science subject physics

Science

1. The Nature of Forces

2. Forces
• A force can cause an
object to start
moving, stop moving,
or change direction.
• Forces combined in
the same direction are
added.
•Forces combined in
opposite directions are
subtracted

3. Balanced Forces
•Forces that are in
opposite direction and
equal in size.
•When forces are
balanced there is no
motion.

4. C. Unbalanced Forces
•Forces that are in the
same direction or in
opposite direction and
unequal in size.
•When forces are
unbalanced there is
motion.

5. II. Friction
•A. Friction – Force
that acts in the
opposite direction of
motion; will cause an
object to slow down
and finally stop

6. B. Sliding Friction
•When solid objects
slide over each other
•Examples –
•Brakes
•Snow board

7. C. Rolling Friction
•Friction produced by
objects such as wheels
and ball bearings.
•Tends to be less than
sliding friction.
•Examples –
•Wheels
•Ball bearings

8. D. Fluid Friction
•Friction when an object
moves through fluids or
gasses.
•Lubricants such as oil and
grease change Sliding
friction into fluid friction.
•Examples –Air resistance
(terminal velocity), water
resistance.

9. Desirable and Undesirable
Friction
Desirable Friction
*Brakes on a car
*Soles on shoes
Undesirable Friction
*Moving parts in car
engine
*Air resistance

10. Newton's First Law of Motion
•An object at rest will
remain at rest and an
object in motion will
remain in motion at
constant velocity
unless acted upon by
an unbalanced force.

11. Inertia
•Tendency of objects to
remain in motion or
stay at rest unless
acted upon by an
outside force.

12. Second Law of Motion
•Shows how force,
mass, and acceleration
are related
•Force = Mass x
Acceleration
(F = m x a)
Units – Newton (N)
N = 1kg x 1m/s
2

13. Third Law of Motion
•1. States that for every
action there is an
opposite reaction.
•2. For every force
there is an opposite
and equal force.

14. Gravity
A. The acceleration of a
falling object is due to
the force of gravity
between the object and
earth.

15. Law of Universal Gravitation
•All objects in the
universe attract each
other by the force of
gravity. The size of
the force depends on
the size of the masses
and the distance
between them.

16. Falling Objects
1.Freefall - All falling objects
accelerate at the same rate
regardless of their masses.
2.Acceleration due to gravity on
earth is due to the force of
gravity between the object and
earth.
3.(9.8 m/s
2
)
For every second an object
falls it will accelerate another
9.8 m/s.
4.m = meters, s = seconds

17. 5. Air Resistance
Air resistance opposes
motion, it is a type of
fluid friction.

18. 6. Terminal Velocity
As an object falls air
resistance gradually
becomes equal to the
pull of gravity, the
object continues to fall
but at a constant
velocity.

19. Weight
1.Weight is the
measure of the force
of gravity on an
object.
2.Weight = mass x
acceleration due to
gravity (w = m x g)

20. Weight
3. Units -
Weight = N (Newton)
Mass = kg (kilogram)
Gravity = m/s
2
(9.8 m/s
2
)
4.
Newton = 1kg x 1 m/s
2