Forces

CSEC Physics Syllabus - Effective for examinations from May - June 2015

Section A - Mechanics

Statics
Forces

Specific Objective 3.1

explain the effects of forces;

Specific Objective 3.2

identify types of forces;

Specific Objective 3.3

determine the weight of objects.

Pixabay

What is a Force?

A force is a push or a pull.

What are the Effects of Forces?

A force may be used to change the shape of, speed up, slow down and/or change the direction of an object. 

Types of Forces

Forces can be categorized into two groups: Contact and Non-contact forces. 

Contact Forces

Applied Force (Thrust)

A force applied to an object by a person or object.

Frictional Force (Friction)

The opposing force exerted by a surface as an object moves across it.

Tensional Force (Tension)

A force transmitted through a string, rope or wire which is pulled tort by forces acting from each end.

Tension is created when a rope attached to a vertical wall is pulled by an Applied Force.

Spring Force

The force exerted by a stretched or compressed spring on an object.

Normal Force (Normal Reaction)

The support force exerted on an object which is resting on another stable object.

Non-Contact Forces

Electric Forces

This is a force of attraction that exists between positive and negative electric charges and a force of repulsion that exists between two or more positive or negative electric charges. This force also exists between electric fields and electric fields and electric charges.

Opposite charges attract each other.

Like charges repel each other.

Magnetic Forces

This is the force of attraction that exists between a north and a south pole and a force of repulsion between two north or south poles of a magnet. This force also exists between magnets and current carrying conductors.

Unlike poles attract each other.

Like poles repel each other.

Nuclear Forces

These are very strong forces that hold particles together in the nucleus of the atom.

The nucleus of the Atom.

Gravitational Force (Gravity)

This is the force of attraction between two or more masses. They are weak but may be sizeable if one of the masses as large as a planet. 

Gravity on the Earth = 9.81 N/kg
Gravity on the Moon = 1.62 N/kg

Finding the Weight of Objects

Definition of Weight:

Weight is an applied force an object applies to a surface due to gravity. The weight of an object varies from planet to planet and with latitude on a given planet. The vector representing the weight of an object is drawn from the center of mass of the object and points vertically downwards.

Symbol:

Weight, W.

Unit:

Newton, N.

Formula:

Weight = Mass × Gravity

W = m × g

Example 1

Steve measured his mass using a bathroom scale and read 75 kg. What is his weight on Earth and on the Moon, if the gravity on the Earth is 9.81 N/kg and 1.62 N/kg on the Moon. 

Solution

Example 2

The Samsung Galaxy S10 has a mass of 157 g. Determine its weight on Earth and on the Moon. 

Solution

Example 3

An irregularly shaped object of density of 272 kg/m³ is placed in a cylinder containing liquid to determine its volume. Its density was determined to be 24 ×10^-6 m³. Calculate the weight of the object.

Solution