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FORCE
Force is a push or a pull which changes a body's state of rest or uniform motion in a straight line. Force is a vector quantity which has both magnitude and direction.
Pushing or pushing a door with force is an example. Force is a vector quantity, meaning it has both magnitude and direction. Newton's second law defines force as the "product of a body's mass and acceleration."
The SI unit of force is newton (N).
A newton is a force which gives a mass of 1kg an acceleration of 1ms-2.
Effects of a force
Force on a body has the following effects;
i. It makes a stationary body move when pushed or pulled.
ii. It changes the direction of a moving body.
iii. It deforms or changes the shape of a body.
iv. It makes a moving body move faster or slower.
v. It stops a moving body.
vi. It changes the speed of a moving body.
Types of forces
The following are types of forces;
1. Frictional force
This is a force that opposes relative motion between two surfaces.
2. Centripetal force
This is the force that keeps a body moving in a circle and is directed towards the centre.
3. Up-thrust force
This is an upward force acting on a body immersed in a fluid.
4. Magnetic force
This is the force that attracts or repels magnetic substances.
5. Electrostatic force
This is a force between two charged bodies.
6. Cohesion force
This is the force of attraction between molecules of the same kind.
7. Adhesion force
This is the force of attraction between molecules of different substances.
8. Viscous drag force
This is the force which opposes motion of body moving in a fluid.
9. Tensional force
This is the pull or compression of the string at both ends.
10. Gravitational force
Note:
Acceleration due to gravity depends on the distance from the centre of the earth and since the earth is not a perfect sphere then acceleration due to gravity is greater at the poles than at the equator because the polar radius is less than the equatorial radius.
RESULTANT FORCE
The resultant force is a single force which has the same effect as of two or more forces acting on a body.
When two or more forces act on a body there is a resultant force, the resultant force may be greater or equal to zero. When the resultant force on the body is zero the body is said to be in equilibrium.
1. Forces acting in a straight line
A. Forces acting in the same direction.
Examples:
1. Two forces of 120N and 250N act on body in the same direction. Find the resultant force on the body
= 370N to the left
2. Two forces of 29N and 34N act on a body as shown below. Find the resultant force on the body
B. Forces acting in the opposite direction
Examples:
1. Two forces of 900N and 250N act on body in the opposite direction. Find the resultant force on the body
Resultant force, F = 250 – (70 + 90)
= 250 – 160
= 90N to the left
2. Forces acting in the opposite direction
Examples:
- Two forces of 900N and 250N act on body in the opposite direction. Find the resultant force on the body
Non - Fundamental Forces
Are the forces in which the two interacting objects are in physical contact with each other
Examples are:-
(a) Kicking a ball
(b) Air resistance
c. Pulling a door
(d) Tension
(e) Compressing a spring
(f) Friction
(g) Elastic forces etc.
Effects of Forces
Forces have several effects on objects. These effects include: -
i. Stretching (tensile)
ii. Torsion
iii. Attraction
iv. Friction
v. Compression
vi. Viscosity
vii. Air resistance
viii. Repulsion
i. Stretching and Restoring
Stretching occurs when an object increases its length when the force is applied to it.
For some objects there is a tendency to return to their original shape and size. This is called restoring force.
For example, when spring is pulled the stretching force elongates the spring
ii. Compression and Restoring
Compressional force is the force which when applied to an object results in decreasing in its volume.
Example when you compress the spring
Restoring force is the force which causes a body to return to its original shape and size
iii. Attractive force
Is the force that pulls objects toward each other.
For example, A Magnet always attracts other objects like iron.
iv. Repulsive force
Is the force that pushes objects against each other.
For example, when the same poles of magnets are closer to each other, they repel
The figures below show an example of attractive and repulsive force
v. Torsional Force
Is a force produced when a solid matter is twisted
vi. Frictional force
Is the force that prevents a body from sliding.
For example, an exercise book cannot slid on top of a table due to friction exists between exercise book and table
vii. Viscous force
Viscosity is the resistance of a fluid to flow.
For example, water has a lower viscous force than cooking oil, since it has less resistance to flow
viii. Air Resistance
Is the force that resists the movement of an object through the air.
Example of this force is viscosity
Factors affecting Air Resistance
a. Size and shape of the body
b. The speed of fluid
c. The density of the fluid
Normal Force
Is the force that acts in equal and opposite direction to the weight of a body
Applied Force
Is the external force that causes the system or body to change position
