Types of Forces

Types of Contact Forces

There are several different types of force. They can be the result of many different situations.

For instance, if you have a ball on a table, and then you tap it, it will move. Depending on how much you tap it, depends on how far the ball will go (eventually going off the side of the table).

This is known as a contact force.

There are several types of contact force, including:

• friction force
• muscular force
• tension force
• normal force
• drag force
• air resistance
• upthrust or bouyancy
• surface tension

Here's a YouTube video from Cognito on the types of force:

In Depth

Friction Force

Friction force arises when there are two objects making a relative motion against each other. When you rub your hands together, they get warmer, right? That's a friction force.

Within this type of force there are two sub-types - static friction and kinetic friction.

Static friction force is the friction that occurs when you have an object placed on a surface.

Kinetic friction force is when the object starts to move over a surface.

Muscular Force

When you move around, your muscles move. This causes a certain amount of friction. Like I said above, rub your hands together and it causes friction. On top of the actual movement of your fingers rubbing together, the muscles within those fingers, your wrists, your arms, etc, all work together to try and make you warmer.

Tension Force

Line two teams of people against each other, with a rope in the middle. Each team moves away from each other, pulling the ends of the rope. Sound familiar? Tug of War is the prime example of tension force. Both teams want to win, by pulling the other over the line in the middle.

The result: the rope in the middle has a lot of force within it. If both teams were to let go of it, the rope would return back to normal elasticity, albeit probably curled up in some sort of circular ball or motion.

Normal Force

Normal force is the contact force exerted on an object when placed on a stable surface. Fill a box with some form of goods, and place it on the top of a table. Now walk away. The general force applied here is that box just sitting there in normal gravity, and there is no form of movement.

Drag Force

Drag force is the process of creating drag while moving through water, or a liquid. If you think of a boat that floats on the surface of the water, it creates a wake. This is the result of the drag force against the hull of the ship.

Air Resistance Force

Air resistance force is the process of something creating air resistance. A common way to explain this is with an aeroplane. It flies. We know that, but what it also does is create drag. If you look in the sky on a nice summer's day, you will see contrails. These are like little puffs of smoke that have been created by the drag force off the top of an aeroplane wing.

Upthrust/Buoyancy

When you go underwater, you return to the surface of the water, because you are buoyant. This is a force that moves you through the water (at depth) to the top.

Surface Tension

Surface tension is how much pressure is added to an object when placed on top of the water, before it breaks the tension and surround the object. If you go to a river during the summer, take a look at what is on top of it. You'll find water skaters - little flies that float on top of the water. They are staying on top due to the surface tension.

Interesting fact: another type of force is known as applied force. When you push a friend on a swing, for example, they will move in the direction you push them.

Types of Non-Contact Forces

Another types of force is called a non-contact force. This is a force we cannot see, or make happen. They just do.

For instance, Earth uses gravity to keep everything on the ground. If we have an item, and it can be 9 out of 10 items, it will drop to the ground when you drop it. There are only a few items that will float (a helium balloon, for example).

Electrostatic force is another type of non-contact force, whereby rubbing a balloon (as an example) against another surface, and then placing it near your hair will make your hair stand on end.

Finally, magnetic force is a force that is not seen. If you put two magnets together, the force will pull them together, depending on how far away the magnet is. This is due to the attraction or repulsion of the magnets.

Resultant Force

As with most end products, force is equivalent to the end result. In the instance of a box placed on a table, a resultant force is the product of two different forces acting together on it. Just add the two forces together, and you get a resultant force. To better explain this, a box that might weight 50N (Newtons) sits on the table. The table itself has a normal reaction force of 50N, which, when you add them together, results in 0N. It is balanced.

Another way to think about it is if you drop the same box from a height, it travels through the sky toward the ground at 50N, and the upward force of air resistance is 20N, overall the resultant force is 30N, downwards.