Chapter 21 Force

Forces
A force is a power which pushes or pulls aa object. It cannot been seen but it can be felt.The effect of a force can be observed. It causes a change in shape,position and speed of the object.

Pull and Push1.We can feel a pull when we pull at both of our wrists.
2.We can feel a push when our palms press against each other.
3.In the above two cases, force cannot be seen, the hand can feel the push and the pull that is applied.

ACTIVITY
Investigate the pull and push force
METHOD
1.Choose your partner as this activity needs a partner.
2.Hold the hand wrist and start pulling.
What can you feel?
3.Push your partner’s hand. What can you feel?
OBSERVATION:
1)Pulling force is felt when pulled.
2)Pushing force is felt when pushed.
CONCLUSION:
Force are felt and observed in pulling and pushing force.

Effects of force
The effect of pushing are:
a) a stationary ball
b) a moving ball

A force can.......
a)move a stationary object
-Force can make a stationary object move.
b)stop a moving object
-A force also stops the movement of an object.
For example, a moving ball will stop if it is caught with hands.
c)make an object move faster or slower
-The direction of motion will change if the force is applied in the direction different from its original direction of motion.
d)change the motion of an object
-Force also can change the speed of an object. A ball can move faster if the force is applied in the same direction as the motion.
e)change the cause the shape of an object
-A force can cause the shape of an object to change. For example, a spring can change its shape and the size when compressed or extended.
EXAMPLE:
· If the spring is pulled, it becomes extended.
· The pull causes the spring to be more elongated.

· If a push is applied on the spring, it becomes compressed.
· The pull causes the spring to become shorter.

Other examples to show on the shape of an object are:
PULL-Rubber band becomes extended when pulled.
PUSH-Plasticine becomes flat when pressed.
-Nail can become dented when hit by hammer.

FRICTION·Friction is atype of force that opposes the movement of an object. Friction exists when two surfaces rub against each other.
·Friction produces heat. It also slows down the motion of he object.
·The ball moves slower and slower and soon stops moving. This is because of the friction between the floor and the ball.

Factors That control Friction1.Friction is influenced by several factors.
2.The rougher the surface, the greater the friction produced. For example, a ball moves slower on grass than on the cemented floor as the surface of grass is more rougher than the surface of cemented floor.
3.A heavier object also produces a greater friction. That is why it is more difficult to move a heavy load than a lighter one.
4.In addition.the shape of an object also affects friction. An object with tapering front end with a smaller surface against airresistance.
5.That is why such objects when released will reach the ground faster than objects which are cuboidal.

Advantages and Disadvantages of Friction1.Friction brings both advantages and disadvantages. Amond the advantages and disadvantages are:
ADVANTAGES OF FRICTION· Prevents us from slipping when running or walking
-EXAMPLE: A wet floor is slippery and has little friction
· Stops a moving vehicle
· Maintains the position of a stationary object
· Produces fire

DISADVANTAGES OF FRICTION·Slows down the movement of of objects
·Damages objects
-EXAMPLE:The sole of shoes becomes worn out
· Produces unnecessary heat

Friction can be reduced by these methods:
·Applying oil,grease or wax
·Using rods,ball bearings and wheels
·Using air cushion