Force in simple terms can be called any interaction that results in a pull or a push. It can change the speed of any object, change the direction, and change the shape of an object. Force can be used to move an object from rest and also to make a moving body stop. It is a vector quantity with both magnitude and direction.
In the English language, we use the word force to signify physical strength or might, for example, air force, armed force, or in sentences like ‘I will force him/her to do something. In mechanics which is a domain of physics, the definition of force is just a pull or a push.
What is the meaning of force according to Newton’s laws of motion?
The exact meaning or expression of force can be understood by looking at Newton’s laws of motion. We can deduce the formula of force and understand what actually force is and what it is not.
- The first law speaks of how only an external force is required to stop a moving object. Also, how a moving object can be stopped by the application of force.
- The second law of motion explains the factors affecting force. Force is directly proportional to the mass of an object and the acceleration of the object.
- The third law explains that forces are exerted in an equal and opposite manner. For every action, there is an equal and opposite reaction. This indicates that force can change the shape of objects.
Examples of force
Examples of pulling force
- Opening a door by the knob involves muscular force by our hands.
- Doing pull-ups in a gym bar.
- Pulling the rope in a game of tug of war.
- Lifting things is a pulling action due to muscular force.
- Horse pulling a cart.
- Apple falling onto the ground is an example of the earth’s gravitational pull.
- The magnetic force of attraction
Examples of pushing force
- A nuclear explosion
- pushing a tree
- throwing a ball in the air
- Kicking a football
- Paper flying by the force of the wind
- Things stopping due to frictional force
- The magnetic force of repulsion
What can a force do?-Effects of force
- Force can move an object from rest
- Force can make a moving object stop
- Force can change the direction of motion
- Force can change the shape of an object
Let us look at each of the points in detail with examples:
Force can move an object from rest
According to newton’s first law of motion, an object in motion should continue to be in motion unless acted upon by an external force. In other words, in the absence of force objects at rest will not move forever. Some of the examples are:
- Our cars move due to the force generated by the engines transmitted to the wheel. The energy stored in the fuel is converted to mechanical force.
- We can walk due to our legs pushing the ground in the backward direction to generate an action-reaction force.
- River water flows from mountain peaks due to the gravitational pull of the earth.
- We are able to throw a ball in the air due to the muscular force of our hands
- We are able to kick the ball to set it in motion because of the muscular force provided by our legs
Force can make a moving object stop:
According to Newton’s first law of motion, an object in motion will continue in motion in a straight line unless acted upon by an external force. In other words, in the absence of force objects will not stop. Some of the examples are:
- We are able to stop a car because of the frictional force between the brake pads and the wheel. In short, the frictional force in the brakes helps us to stop a moving vehicle.
- When we catch a moving ball, we stop the motion and bring it to rest. The muscular force generates enough force to stop the motion of the ball
- Even without any external force, a moving thing comes to a halt. Have you wondered why? It is due to the frictional force generated during the sliding of two bodies. You can watch this video on life without friction to learn more.
Force can change the direction of a moving body
According to Newton, an object in motion should continue in motion in a straight line unless acted by an external force. Without force, we won’t be able to turn. Some of the examples are:
- In a game of soccer, we are able to pass the ball quickly due to the muscular force in our legs
- In tennis, a person is able to change the direction of the ball depending on the angle of force applied by the racquet onto the ball.
- When we throw a basketball onto the board we get a rebound. This is due to the action-reaction force generated by the board, which changes the direction of the basketball.
Force can change the shape of an object
Have you ever crushed a tin can? You can feel the force in you. Force can deform or change the shape of objects. Force can be used constructively, like in pottery or destructively in breaking things around.
What is the formula of force?
Force = mass * acceleration [force is a vector quantity]
The direction of force is also important to be discussed. Imagine the following two cases to understand the importance of the direction of force and how the net force work.
Case 1: Imagine 2 people pushing a car from opposite sides with the same force. [Car will remain in the same position resulting in no impact] Net force is zero because the opposite and equal values of force cancel out.
Case 2: Imagine 2 people pushing a car in the same direction. [Car will move faster in the intended direction of motion]. Net force will be 2F because both forces since they are in the same direction will get added up.
The common force acting on a body is the weight of the body due to gravity. The weight of an object is equal to mass*gravitational constant [gravitational constant(g)=9.8m/s2]
What is the unit of force?
The SI unit of force is Newton or Kgm/s2. Si unit of force is Newton generally represented by the symbol N. Other units of force include pound-force, kip, poundal, Dyne, and ton-force.
1 Newton is the amount of force required to move an object weighing 1 kg for 1 meter in a second.
On what factors does the impact of force depend?
The force depends on the direction of the application. If suppose force is applied at an angle then the component of the force will determine the impact of the force on the object. If Force is applied in the opposite direction of intention then it is called a decelerating force.
Force is directly proportional to the mass of an object. The heavier the object the more force is required to move the object. For example, the gravitational pull, which is a force, is directly proportional to the mass of an object. The more the mass, the stronger will be the gravitational pull.
Force is directly proportional to the acceleration of the object. A car at 50 Km/h will have more impact in an accident compared to a similar car moving at 20 Km/h.
What are the different types of forces?
Based on contact, a force can be classified into:
- Contact force: Muscular force, air resistance, tension, reaction force, and normal force
- Non-contact force: Gravitational force, magnetic force, electrostatic force, and nuclear force
It is possible for a combination of forces to be acting on a body. Like, gravitational force, frictional force, and muscular force can all act together on a body. Let us look at each one of these forces in detail with examples.
What are Contact forces?
The forces which arise only when two bodies come in contact are called contact forces. There are different types of contact forces. Here below we discuss 7 types of commonly found contact forces.
Applied force/Muscular force
This is the force experienced when pushing or pulling an object by using our muscles. All our gyming activities and regular day-to-day activities involve muscular force. In fact, all the activities that we humans do directly without the help of machines are muscular forces.
Normal force
The normal force is the component of force acting in the perpendicular direction when two bodies are in contact. You can experience normal force only when in contact. In a daily case of us standing on the ground, the normal force is the reaction to our weight exerted on the ground.
Reaction force
For every action, there is an equal and opposite reaction force. For example: while you jump you apply a force on the ground in order to be propelled up. The ground provides an equal force in the upward direction in order for you to jump.
Air resistance
Air resistance is a resistive force experienced by a body moving in the air. It acts in a direction opposite to the motion of the body. It is somewhat similar to frictional force, but the force of friction is generally referred to when there is a contract between two solid bodies.
Tension force
It is the force developed in a wire, rope, or threadlike object along the axis due to some kind of stretching or pulling force. Example: Imagine a tug of war. Poor little thing it gets stretched badly, that’s tension.
Tension is the same as force. The only difference is that it is applied axially across a one-dimensional object like a rope or thread. So the formula is mass*acceleration. A few examples of tension forces are discussed below.
- Tension developed in a rope during the tug of war.
- Tension developed on the handles of bags.
- Tension developed in the strings holding a swing.
- Tension in the rope of pulleys while drawing water from wells.
Frictional force
The force of friction acts to oppose any motion during the sliding of two objects. It acts opposite to the direction of force applied. It is called fluid friction in a fluid setting.
Spring force
Spring force is the force generated by a spring when it is stretched or compressed. Both during the pulling and pushing action, force is exerted on the body.
The formula of spring force: F = -K*Δx,
Where k is the spring constant and Δx is the displacement of the spring from its equilibrium position. The sign of the force is negative because it acts in the opposite direction to the force applied initially.
Why Is tension a contact force?
Tension is developed only when we apply force on the string or cables during contact. Without the force applied by contact, there will be no tension developed in strings automatically.
Why is air resistance considered a contact force?
Yes, because the body comes in contact with air, so air resistance comes under contact forces. Without the contact you will not have this air resistance, imagine you are in space, there will be no air resistance there.
What is a non-contact force?
Non-contact forces are forces that are exerted without any physical contact. Non-contact forces are of different types: gravitational, magnetic force, electrostatic force, and nuclear force. Here below we discuss each of them with relevant examples.
Gravitational force
Gravitational force is a pulling force that acts between two bodies that have mass. Anybody who has mass will experience gravitational force. This force does not push, it always tries to pull an object towards itself. Examples of gravitational forces are listed below.
- falling down of apples from the tree
- river flowing down from mountains
- the orbital motion of the Moon around the Earth
- High and low tide in seas
Magnetic force
Magnetic forces are the forces exerted by magnetic materials or by moving charged particles. Not all materials can be magnetized. Magnetic forces are both attractive or repulsive in nature. In other words, they can pull or push. The area around the magnet or moving charged particles where the magnetic effects can be felt is called a magnetic field. The unit of the magnetic field is called Tesla. Some of the examples are repulsion or attraction between magnets, iron nails attracted towards the magnet, etc.
Electrostatics
The electrostatic force is the force exerted due to the charged state of an object. In order words, it is the force between two charged objects. Electrostatic force can be attractive or repulsive in nature. Like charges repel each other and unlike charges repel each other. Some of the everyday examples of electrostatic forces are listed below.
- Balloon attracted towards your T-shirt
- An electron moving around the nucleus in an atom
- The flow of electricity from high potential to low potential.
Nuclear force
An atom is comprised of an electron and a nucleus. The nucleus has neutrons and positively charged protons. The force that binds the neutrons and protons together is called nuclear force. Since there is no contact between the particles, this is a type of non-contact force. This force has a short range of influence but is the strongest of all forces. Examples of nuclear forces are listed below
- The force of a nuclear bomb
- The energy produced by the nuclear power plant
- The attraction between proton and neutrons
Quiz on force
What is the difference between energy and force?
Energy is something that a body has within itself. Whereas, force is not something that is within the body. Force is something that is a result of energy. Force is something that is active and energy is something that is stored.
What is the strongest force?
The nuclear force is the strongest force known in the universe. It is the reason that nuclear force is chosen to create weapons of mass destruction.
What is the weakest force?
Gravitational force is the weakest force known in the universe. But, the gravitational force is directly proportional to the mass of an object. So, for an object with a large mass like Earth, the gravitational force will be very high.
What is a balanced force?
A situation of balanced forces is created when forces are acting in the opposite direction with equal magnitude. Example: the normal force and the weight of an object. When the forces acting on a body are balanced then the object will be either in a state of rest or in uniform motion. There will be zero acceleration on such an object. You can see examples of balanced forces in our daily lives.
- The normal force and the weight of an object
- When you push a wall. The action-reaction forces are equal and cancel out each other.
- Force applies to an object with a magnitude less than the limiting friction. The frictional force will cancel out the applied force.
- Objects hanging on a wire or string. The tension in the string cancels out the downward force exerted by the hanging object. Hence the object is in a stationary state.
Force in a curvilinear motion
When an object is in a curvilinear motion(motion in a curved path) then the object tries to remain in a straight path due to inertia. This nature tries to push the object away from the path. This is called the centrifugal force. At the same time, there is also a force that acts to pull the object towards the center. This is called the centripetal force. In a rectilinear motion(straight line motion) these forces are absent as the radius of curvature is zero.
Roads are generally banked at an angle at turns to avoid this centrifugal force that pushes the cars off the roads. You can read more here.
Solving numerical problems on force
When calculating force, we assume the entire force acting on a body to be concentrated at the center of gravity. Because any force acting on a body acts on the whole body. But for simplicity, we concentrate all the forces at a particular point.
Resolution of forces in an inclined plane
Sometimes forces might act at an angle like in an example of an inclined plane. Then the component of the force acts on the body. In the example above you can see that the component of the weight of the object acts to balance the normal force. Also, the component of weight tries to pull the body down against the action of the kinetic frictional force.
Is Pressure a force?
The pressure is the amount of force applied per unit area. It is the impact of force on a body. It is not a type of force. When you apply force to an object then pressure is also applied to it. Pressure can also be called the distribution of force over a body.
See also
- What is force?
- What is frictional force?
- What is the formula of force?
- 5 Effects of force
- Balanced forces
- Non-contact forces
- Tension force
- Unit of force
- 10 Examples of unbalanced forces
- 20 Examples of balanced forces
Research
Robots are generally made up of many small parts out of which some are flexible and can absorb external forces only up to a certain limit beyond which they may break. So, sensors are very important in robots to sense the force so that it doesn’t exceed the maximum tolerable limit. In humans, our skin can sense and give information to our brains and take decisions. Here in this article authors have designed a low-cost robotic arm with a virtual force sensor.
In this article, the authors have proposed a robot-assisted pelvic balance trainer (RAPBT) whose range of motion can be controlled by the patients via force field. A detailed force analysis is done by the authors.
Ice formation on rotor blades of airplanes is a huge challenge for aerospace engineering. The authors here have studied the relationship between the centrifugal force and the icing on the rotor blades through some simulations methods.
