2.5effect of force(latest)

8/7/2019 2.5Effect of force(latest)

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FORCE AND MOTIONFORCE AND MOTION

2.5 Understanding the

effects of a force



Previous LessonPrevious Lesson

± Define the momentum of an object

± State the principle of conservation of momentum

States that the total momentum is constant if no

external f orce is acted upon the system.

OR

total momentum before collision = total momentumafter collision



Learning ObjectivesLearning Objectives

At the end of the lesson, a student is able to:

� describe the effects of balanced forces acting

on an object.

� describe the effects of unbalanced forces

acting on an object.

� determine the relationship between force,

mass and acceleration F = ma.

� solve problems using F = ma.



ForceForce

� A force is push or pull exerted on an object.

� Force is a vector quantity that has magnitude and

direction.

� The unit of force is Newton ( or kgms

-2

).

weight

Tension Buoyant f orce

weight



Eff ects of a Eff ects of a ForceForce

� A force can change the shape of an object.

� A force can change the original state of motion of anobject.

HOW ?



FForceorce can alter the object in can alter the object in

aspect of ...aspect of ...



Why this

object cannot

move..?

Now I can movethis object but

why..??



Balanced ForceBalanced Force

� When the forces acting on

an object are balanced,they cancel each otherout.

� The net force is zero.

� Fnet = 0

Balanced force

No movement



The f orces acting on an object at The f orces acting on an object at

restrest

� A cup of coffee is put on a

table

� The weight, W of the cup is

acting downward vertically.� At the same time, an

opposite and equal force

known as normal reaction,

R from the surface of the

table acted on the cup.

� Therefore, the cup remain

at rest.



The f orces acting on an object moving at The f orces acting on an object moving at

constant velocityconstant velocity

� A plane is flying horizontally

with constant velocity at

constant height.

� The engine provide aforward trust, T.

� The wind and air resistance

provide a drag, F.

� The wings of aeroplane

provide a lift, L vertically to

balance its downward

weight, W.

Lift

DragTrust

Weight



Unbalanced ForceUnbalanced Force

� When the forces acting on

an object are notbalanced, there must be a

net force acting on it.

� The net force is known as

the unbalanced force

Unbalanced force

Movement




� When a footballer kicks a

fast moving ball towards

him, the ball bounces off

and moves in other

direction.

� The unbalanced force

causes the ball to change

its direction




� When the engine of a moving

car is turn off, the car will slow

down and finally stop.

� The net force due to frictional

force is acting against the

direction of the motion of car.

� It causes the car to decelerate.

Pulling force

Frictional force



Net f orces / Resultant f orcesNet f orces / Resultant f orces

� Is the overall f orce resulting from the

combination of the individual f orces acting

on the object.� Balanced f orce : Net force is zero and there is

no change in motion.

� Unbalanced f orce : Net force is the diff erence between the f orce acting in opposite

directions and causes an acceleration



Newton's 2nd Law of MotionNewton's 2nd Law of Motion

� Newton's Second Law:

When there is a net f orce acting on an object,

the object will accelerate.

� Newtons Second Law of Motion:

The acceleration of a body, a, is directly proportional to the net force acting on it, F ,

and inversely proportional to its mass, m:

F = ma



The Relationship between Force, The Relationship between Force,

Mass & AccelerationMass & Acceleration



The Relationship between Force, Mass &The Relationship between Force, Mass &

AccelerationAcceleration



BRAINSTORM...



� A box of mass 150kg is placed on a horizontal

floor with a smooth surface; find theacceleration of the box when a 300N force is

acting on the box horizontally.

� A object of mass 50kg is placed on a

horizontal floor with a smooth surface. If the

velocity of the object changes from stationary

to 25.0 m/s in 5 seconds when is acted by a

force, find the magnitude of the force that is

acting?



Learning OutcomesLearning Outcomes

Students should be able to:

� describe the effects of balanced forces acting

on an object.

� describe the effects of unbalanced forces

acting on an object.

� determine the relationship between force,

mass and acceleration i.e. F = ma.

� solve problems using F = ma.



Eff ects on object when there is.Eff ects on object when there is.

Balanced Force

� The object will remain

stationary[ velocity = 0] or

� Continue to moves atconstant velocity [ a = 0]

Unbalanced f orce

� Can cause a body to

- change in shape

- move from rest

- accelerate or decelerate

- change it direction while

moving

- stop from moving

2.5effect of force(latest)

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