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A force is a push or a pull acting upon an object. When we talk about different types of physical forces we will use the word exert. Exert means put to use or exercise. (For example, all objects exert gravitational forces.)

All forces exist as a result of interaction between objects. These interactions occur on a macroscopic level between objects that can be seen with the naked eye. These interactions also occur on a microscopic level between elementary particles of matter. Elementary particles are the smallest structural units of matter. They are very small and can be seen only through a very powerful microscope.

There are many types of physical forces. All objects in the universe are usually affected by several different forces at once. This chapter looks at the type of force called applied force.

What is applied force?

Force is a vector quantity. Vector is a physical quantity described by magnitude (meaning the strength of the force) and direction. Applied force means the force with which an object has been pushed or pulled by another object. In physics, objects include atoms, planets, people, comets, machines, machine parts and many other objects.

The force with which a comet hits another comet is an applied force. When you ride your bike, you apply force to the bike's pedals, which pulls the chain, which in turn moves the bike's wheel. When you mould a piece of modelling clay, you apply the force of your hand to change the shape of the clay. Actions like cracking an egg, throwing a ball, moving furniture or pushing a button also involve applied force.

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Combination of different physical forces

All objects are affected by several different physical forces at once. The force that is the strongest will define the change of an object. The change might mean a change of shape, position or speed of an object. Now, let's look at an example of the combination of different physical forces, where the applied force is the strongest force.

Example: a rolling ball
Object of study: a ball
Forces affecting the object: applied force (a push), chemical bonding forces, gravitational forces, the force of atmospheric pressure, the force of air resistance and frictional force.

Applied force

In our example, a ball started rolling because someone pushed it with his or her hand. In other words, someone has applied the force of his or her hand to the ball. The energy or force used to push the ball is the result of complex chemical reactions that occur inside our bodies. This energy can be converted into different types of forces. In our example, it was converted into the force that was applied to the ball.

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Chemical bonding forces

All objects are made of very small structural units, called molecules. Molecules hold on to each other with chemical bonding forces. Solid materials have stronger chemical bonding forces than gases and liquids. In our example, a ball is made of a solid material, so it has strong chemical bonding forces.

Gravitational force

Gravitation is a force of attraction between all objects in the universe. All objects in the universe are affected by the forces of gravitation. The larger the object is, the stronger its force of gravitation. On Earth, the largest object is the Earth itself, so all objects are attracted or pulled down towards it. In our example, the ball stays on the ground because of the gravitational force of Earth.

Atmospheric pressure

All objects on Earth are affected by the force of atmospheric pressure. The force of atmospheric pressure is created by the weight of air. Air is not the name of a chemical element or gas. Air is a non-scientific term for a mixture of many different gases. The atmosphere is a layer of different gases surrounding our planet. Even though air seems weightless, it does have a weight. The Earth's atmosphere is about 500 kilometres deep. That is a lot of air! This air pushes down, with its weight, everything on Earth, creating atmospheric pressure.

Air resistance force

Air resistance force affects all moving objects on Earth. As objects move, the air pushes against the object, slowing down its movement.

Frictional force

Frictional force is a force that acts between the surfaces of moving objects. The intermolecular forces between molecules of different surfaces create frictional force. As the ball rolls, its surface rubs against the surface of the floor. Both surfaces appear smooth to the naked eye. If we look at the surface of the ball and the surface of the floor under a magnifying glass, we notice that both surfaces are rough and bumpy. These bumps create friction between the surfaces that slows down the rolling ball.


In our example, the applied force of the hand that pushed the ball is the strongest compared with all other forces affecting the ball. The applied force makes the ball roll.

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Question 1/5

1. Approximately how deep is the Earth's atmosphere?

500 kilometres

5 kilometres

18 kilometres

2000 kilometres


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