__"Force"__
1.
A

**force**is a**push**or a**pull**:
i.
which can cause an object to

**change**its**shape**(e.g. plasticine)
(In upper
secondary

**,**you will learn about the**relationship**between**the****force**applied on a spring**and its****extension or compression**as summarized by**Hooke’s Law;**and**elastic potential energy –**please see: Form 4 Physics Chapter 2)
ii.
which can cause an object to

**change**its**state of motion**in terms of:
1.

**position**(pushing or pulling a trolley)
2.

**speed**(blowing a moving ping-pong ball in the direction of its motion)
3.

**direction**(blowing a moving ball at an angle to its direction of motion)
(In
upper secondary

**,**you will learn about the effect of**force**on the**state of motion**of a body in greater details)
iii.
which can produce

**turning effect**known as**moment**of a force.
(

**Moment**(N m) =**Force**(N) x**Perpendicular distance**(m) from pivot to the force; and levers operates on principle of moments – It iss 1 of the**simple machine**– 3 types of**levers**: 1^{st}class, 2^{nd}class and 3^{rd}class levers)
2.

**Forces**which exist**in nature**include:
i.

**Gravitational force**- a mass in a gravitational field experiences gravitational force. Now, in Form 4,**you will learn about****gravity**in greater details.
ii.

**Magnetic force**- a magnet in a magnetic field experiences magnetic force: Like poles repel and unlike poles attract. You will learn more of this**in Form 5 Chapter 3**on “**Electromagnetism**”.
iii.

**Electrostatic force**- an electric charge in an electric field experiences this force.**This**will be covered**in Form 5 Chapter 2.**
iv.

**Frictional force**– It exists between a mass and the surface in contact.**This**was covered**in Form 2 Chapter 7**:
1.
The

**direction of frictional force**is always**against**the**direction**of**motion**of the mass.
2.
The

**magnitude of frictional force**depends on:
a.
The

**mass**of the body – the heavier the mass, the higher the friction; and
b.
The

**roughness**of the surface in contact – the rougher the contact surface, the higher the friction:
i.
To

**increase friction**, roughen the contact surface – use of rubber pad, deep treads on shoes and tyres.
ii.
To

**reduce friction**, smoothen the contact surface – use of oil and lubricants; ball bearings, rollers and wheels; move on air or magnetic field (maglev); streamlined body and so on.
3.
One way to

**measure force**is by the use of**spring balance.**
4.
The SI

**unit of force**is**newton**(N)
5.

**Work**is done when an object is moved by a**force**through a**distance**in the**direction of the force**:**Work done**(J) =

**Force**(N) x

**Distance moved**(m)

6.

**Power**is the**rate of doing work**:**Power**(W) =**Work**(J) /**Time**(s)
7.
The

**turning effect**of a**force**about a pivot is known as the**moment of**a**force**which is the**product of**the**force**F and the**perpendicular distance**l of the force from the pivot
Moment = Force F x Perpendicular
Distance l

8.

Sum of anti-clockwise moments = Sum of clockwise moments**Moments**about a pivot are**balanced**when:
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