Forces

Forces

Introduction to Forces

Forces are in play all around us. Objects that are hanging, sitting, balancing, moving, and spinning are all using some kind of force. Forces come in different forms, and they all result in something.

Let us start the lesson with this short scenario —

“Milly opened the fridge and brought out a chilled can of soda. In a hurry, she slammed the door, opened the soda, and gulped it down. She crushed the can in her hand and threw the empty can into the bin.”

Milly applied force in many of her actions (highlighted actions). Her actions involved some force to lift, open, turn, move and even change the shape of something.

Force, together with its various types is applied in almost every single activity in our lives.

Pushing the shopping cart, pulling the baby stroller, lifting weights at the gym, eating, and many other things involve the use of some force.

Can you think of the many ways in which you have applied a force to get results?

Forces can:

Change the direction of an object. You can pull the leash of your dog to make it change direction.

Turn things. A natural force like wind can turn the blades of a wind turbine to generate electricity.

Change the shape of something. Next time your mum makes dough for bread, watch her change the shape of the dough with the rolling pin.

In this lesson, we shall look at Forces in detail and how forces change the shape of objects, get things moving, cause moving objects to speed up, slow down or stop and change the way things move. Weight, pressure, and turning moments are all the result of forces too. Ready?

What is a force?

A force can be a push or a pull. It is not something you can see or touch but can see it in action. Forces can be measured using a device called a force meter. The unit of force is called the Newton. It is represented by the symbol N. A force of 2N is smaller than 7N.

A force usually results from an interaction. The interaction can be a physical one or a non-physical one. Forces resulting from physical interaction are called Contact Forces, and examples include Frictional, Tension, Air Resistance, and Spring force.

Measuring forces

A force resulting from non-physical interaction is called Action-at-a-distance force and examples include gravitational, electrical, or magnetic force.

Force meters (right illustration) contain a spring connected to a metal hook. The spring stretches when a force is applied to the hook. The bigger the force applied, the longer the spring stretches and the bigger the reading.

A Force diagram

A force diagram is used to show the forces acting on an object. An arrow, with a name, length and direction is used to represent a force.

In a force diagram, the longer the arrow, the bigger the force. See this illustration:

What is Mass?

Every object is made up of matter (Matter is anything you can touch physically) The more matter an object has, the bigger it is, and the more mass it has. 

Mass is measured in kilograms, kg, or grams, g. Things that have a big mass are harder to move. They are also harder to stop when they are in motion than objects with less mass.

Mass is how heavy something is without gravity. It means the mass of an object is the same on earth and in space (or other planets)

A 100gm ball will be 100kg everywhere, even on the moon. This fact is not the same for weight. The weight of an object can change at a different place, such as on the moon.

In the previous illustration, notice how the mass of an astronaut remains the same, while his weight is smaller on the moon as a result of less gravity.

Mass is NOT the same as weight. The difference is that weight is determined by how much something is pulled by gravity. If we compare two different things to each other on Earth, they will both be pulled by the same gravitational force, so the one with more matter will weigh more.

What is Weight?

Weight is a force caused by gravity. Because it is a force, it is also measured in Newtons (N). It is the gravitational force between the object and the Earth. An object will have a greater weight if it has more mass.

All over the world, people read the weight of objects with kilograms. That is not correct. It is done only because it is easy for people to grasp. The proper scientific unit of measurement is Newton, and it is written as N.

As mentioned on the previous page, the weight of an object is the same everywhere on earth because the object is under the same pull of gravity. In Space, there is no gravity, so the object will not even sit on the scale at all. It will just stay in suspense. Technically speaking, there is no weight in Space.

Weight is the vertical force exerted by a mass as a result of gravity. Gravity is a key concept here. Weight is dependent on it. In other words, it is the strength of the gravitational pull on the object.

Gravity on the Moon is less, and that means an object will weigh less on Moon than on earth.

An object’s weight (W) can be determined by the product of its mass (m) and the magnitude of the local gravitational acceleration (g), thus W = mg.

An object with a mass of 1 kg has a weight of about 10 N, everywhere on earth.

“Mass does not change whether it is measured on Earth or the ISS. Weight can change depending upon the gravitational pull such as on the Moon where weight is reduced to one-sixth that of on Earth.” 

Apparent weight

Sometimes the scale can record the weight of an object and get it wrong. Here is a simple test: The next time you stand on a scale, you will notice that your weight will be slightly more if you try to jump on it. This is because you put more force downwards, in addition to the original force of gravity. This is apparent weight, and it is a measure of downwards force, not the weight from gravity.

What is Gravity?

All objects have a force that attracts them towards each other. This force is called gravity. Even you, attract other objects to you because of gravity, but you have too little mass for the force to be very strong.

The gravitational force increases when the masses are bigger and closer. This means that the gravitational force on Moon is less than on earth because Moon has less mass than Earth.

Did you know?

Does gravity also hold the planet earth and other planets in their orbits around the sun?

Good examples of very massive objects that possess gravitational force include the moon and other planets. Consider the earth on which humans live. Everything tends to fall on the ground and stays there. If you jump, you came down again. Throw a ball upwards, and it will surely come down.

more to come