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VIDEO OF MOTION
What cause motion….?
FORCE
A force also can cause:
a. a moving object to change its speed
c. a moving object to change its direction of motion
d. an object to change in size and shape
THE EFFECTS OF A FORCE
FORCE
1. A force is a pulling or a pushing action on
an object.
2. We make use of forces in our daily life all
the time.
3. Forces have magnitude and direction.
4. The unit of force is newton (N) or (kg m s-2).
5. A force is not visible but the effects of
forces which can be observed.
Balanced Force:
The effects of balanced forces on object:
1.An object may have several forces
acting on it. If the forces are in
balance,
they
cancel
each
other
out. Then, the object behaves as if
no force is applied to it (net force
or resultant force is 0).
2. With balanced forces on it,
an object is either at rest,
or moving at a constant
velocity. (net force or
resultant force is 0).
EXAMPLES:Balanced Force
1. Balance forces on a stationary cup
Another ex.
2. Balance forces on the aircraft result in it
moving at constant velocity
Another Ex.
Unbalanced Force:
The effects of unbalanced forces on object:
1.An object will accelerate when forces
acting
on
it
are
not
balanced.
how to know balanced force---- it has
net force (resultant force).
EXAMPLES:Unbalanced Force
Example
Another Example
Relation Between Force, Mass,
and Acceleration:
A Question
SOLVING PROBLEMS
1. When a force acts on a mass of 3 kg, the
resultant acceleration is 2 m s-2. Calculate
the force………
F (N)
3 kg
a = 2 m s-2
Solution:
F=ma
m = 3 kg
a = 2 m s-2
F = 3 kg 2 m s-2
F = 6 kg m s-2 = 6 N
2. Azhari applies a force of 50 N to move a 12
kg box at a constant velocity. What is the
frictional force acting on the box?
12 kg
F1 =50 N
f
Solution:
Constant velocity ------ acceleration, a=0
Net force in the direction of velocity, F = F1 - f
= 50 N - f
from F = ma
50 N – f = 12 kg 0 m s-2
f = 50 N – 0 = 50 N
3. What force is required to move a 2 kg object with an
acceleration of 3 m s-2, if:
a. the object is on a smooth surface? (f=0)
b. the object is on a surface where the average force of
friction acting on the object is 2 N?
Solution:
a. From F = ma
F1- f = m a
F1- 0 = 2 kg 3 m s-2
F1 = 6 N (a force of 6 N is required to accelerate the object at 3 m s )
-2
b. Net Force (F) = F1 – f = F1 – 2 N
From F = ma
F1 – 2 N = 2 kg 3 m s-2
F1 = 6 N + 2 N = 8 N (a force of 6 N is required to accelerate the object at 3 m s-2)
summary