What Is Meant by Force?

Force is defined as an external cause that changes or tends to change the state of the body once applied. If the body is in motion, it comes to rest, and if at rest, then it will come to motion. It can also cause a change in the direction, shape, size, etc., of the body. 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."

Example: The fact that a push or a pull is referred to as a force should be emphasised as a primary focus of your instruction at this level. There are several instances of forces in our daily lives. For example: weight force (the weight of something). It is the force exerted by a bat on a ball, and the power of the hairbrush on the hair during brushing.

Definition of Force

Force is defined as the pushing or pulling of an item. Push and pull are caused by the interaction of two things. Force may also be expressed using terms like stretch and crush.

A force is an external agent that may change the condition of rest or motion of a body. It has a magnitude as well as a direction. The direction of the force is the place where force is applied, and the application of force is the location where force is applied.

The Formula of Force

The vector product of mass (m) and acceleration (a) expresses the quantity of force. The equation or the formula for force may mathematically be stated in the form of :

\[F = ma\]

Where \[m\]= mass, \[a\]= rate of acceleration

It is expressed in Newtons (N) or kilograms per square metre per second\[(Kgm/{{s}^{2}})\].

Unit of Force

The force applied on an object is measured in terms of Newton and dyne. Force is measured in dyne in the centimetre gram second system of unit (CGS unit). It is represented in Newton (N) in the standard international system of units (SI unit).

Dyne and Newton are related to one another. We can convert the value of force in dyne and newton using the relationship between them. The value of dyne in terms of newton and vice versa is as given below:

1 dyne = \[1{{0}^{-5}}~\]newton

1 Newton =\[~1{{0}^{5}}~\]dyne

Newton: 1N can be defined as the force required to move an object with a mass of 1 kg at an acceleration of \[1\text{ }m/{{s}^{2}}.\]. It is represented by letter N. Mathematically, we write:

\[\mathbf{1N}=1kg\times 1m/{{s}^{2}}\]

1 Dyne: It is the force required to course an object with a mass of 1 gram at an acceleration of 1 cm/s2. Mathematically we write:

\[1~dyne=1g\times 1cm/{{s}^{2}}\]

How Force Can Change the Shape of an Object

When a force is exerted on an item, it might change form by bending, stretching, or compressing-or by a combination of all three.

Force can Change the Shape

Compression forces that change the shape of objects include

• Forces acting on the walls of an inflated balloon when it is pressed between our hands

• The force required to roll chapati or roti dough

• The force that is exerted on a spring or a rubber band when it is stretched

• The force created by a collision between two moving vehicles

Effects of Force

Forces acting on a body can change the shape of the body, accelerate or decelerate it, give motion to the static body, or stop the motion of the dynamic body.

The force effect can be explained by the following:

• The force either increases the speed of a moving object or moves a stationary object.

• A force can either stop or reduce the speed of a moving object.

• The force effect causes the object's direction to change.

• The object's shape and size are altered by force.

Force Can Change the Direction of a Moving Object

How can force be used to change the direction of a moving object? When an external force acts on a freely moving object, its direction will change.

Some examples are given below:

• When you hit a cricket ball, its direction changes.

• When a batsman hits the ball with his bat, the speed of the ball changes.

• When a person applies the brakes in a car, the vehicle comes to a stop with a decrease in speed.

• The speed of the ball decreases when the fielder catches it.

• When we pull the trolley, its speed increases.

Force Can Change the Speed of a Moving Object

When a force is applied to a body, the body accelerates and acceleration alters the body's speed. A force may modify the speed of a moving item, the direction of a moving object, and the form and size of an object, but it cannot change the composition of a moving object.

Some examples are given below:

• When a driver accelerates his car while it is in motion, the vehicle's speed increases.

• When a person uses the brakes in a car, the vehicle comes to a complete stop with a drop in speed.

What a Force Can Do

Forces may cause things to accelerate, decelerate, stop, start, change direction, shape, or even spin. Let’s discuss how it does so!

• Change Direction and Accelerate: Imagine kicking a ball that is slowly approaching you. It will not only go quicker (accelerate), but it may also change direction if you hand it to someone.

• Stop: A force acting on an object causes it to change shape or size, begin or stop moving, accelerate or decelerate. When two objects interact, they exert a force on each other; these exerted forces are equal in size but opposite in direction. Eg: Imagine a goalie using power to deflect a ball that is heading towards him.

• Get Moving: When a force pushes or pulls on an object, it moves in the same direction as the force. The greater the acceleration, the greater the force and the lighter the object. It can also cause something to slow down, accelerate, or change direction.

• Shape Change: When a force acts on an object, it can change shape by bending, stretching, or compressing - or by a combination of all three. Changing the motion of objects is the responsibility of forces. The shape of an object can change if more than one force is present.

• Turning: Forces are required to turn or spin things. When left to their own devices, moving objects move in straight lines. It takes a lot of force to get them to turn in a circle instead. Larger forces are required to turn heavier objects, spin them faster, or make them turn in tighter.

Solved Problems

1. Michael uses 30N of power to push a 2kg box to the left. Annie uses 40N of force to push the same box to the right. What is the box's net force?

Possible responses:

a)1.33N

b)10N

c)−10N

d)0.75N

Ans. We sum together all the forces to get the net force:

\[{{F}_{net}}={{F}_{Michael}}+{{F}_{Annie}}\].

Since force is a vector, the direction of action is important. We shall turn leftward motion into a negative and rightward motion into a positive. Michael is pushing to the left with\[30N\], hence his force is\[30N\]. Annie was pushing to the right with\[40N\], thus her force will stay 40N.

We can get the net force by summing the individual force together.

\[{{F}_{net}}={{F}_{Michael}}+{{F}_{Annie}}\]

\[{{F}_{net}}=-30N+40N\]

\[{{F}_{net}}=10N\]

2. Aimee's toy car weighs 2 kg. How much force should she apply to the car in order for it to go at an acceleration of\[8 m/{{s}^{2}}\]?

Ans.

Given:

m (toy car mass) = \[2\] Kg

a = \[8m/{{s}^{2}}\](Acceleration).

F is Force to be applied by Aimee = \[m\text{ }\times \text{ }a\]

= \[2\text{ }Kg\]× \[8\text{ }m/{{s}^{2}}\]= \[16\text{ }Kgm/{{s}^{2}}\]= \[16\] N.

3. To accelerate a 1000-kilogram truck at 4.00 m/s2, how much net force is required?

Ans.

Given:

a = \[4.00\text{ }m/{{s}^{2}}~\]

m =\[1000\text{ }kg\],

Therefore,

F = ma

=\[1000\times 4\]

= \[4000\]N.

Summary

Force is defined as an external cause that changes or tends to change the state of the body once applied; if the body is in motion, it comes to rest, and if at rest, then it will come to motion. It can also cause a change in the direction, shape, size, etc., of the body. It might be deduced that when the direction of force is in the direction of motion, the speed of the object rises; when it is in opposition to the direction of motion, the speed of the object decreases. Moreover, force does not necessarily have to modify the condition of motion.