In this video, we're going to explore two different types of force, contact forces and non-cont forces. And we'll look at some examples of each. First though, we need to be comfortable with the term force itself. We can describe a force as a push or pull that acts on an object due to its interaction with another object. And we measure force in newtons. For example, when a hand, which is one object, pushes a box, which is another object, it exerts a force like 5 newtons. As well as this magnitude, though, which we're measuring in Newtons, forces also have direction. So we could say that this force is acting to the right. This means that forces are classed as vector quantities because they have both magnitude and direction. Now all forces can be divided into two different groups contact and non-cont forces. And the key difference between the two is that contact forces are those where the two objects are physically touching. Whereas non-cont forces are those that don't require the two objects to be touching. For example, the friction between this board and the sand is a contact force because the board and the sand have to be touching for the friction to act. Similarly, air resistance is a contact force because the object, in this case, a dog's face, has to come into contact with the air particles in order to feel the resistance. Tension is a bit more difficult to explain, but it's basically the pulling force that's being exerted through the rope. The last contact force to know is the normal contact force, which is also sometimes known as the reaction force. In this picture, we can see a rock on a table. And because the rock has mass, it will be exerting a force downwards, which is its weight. To keep it in position though and stop it from falling, the table must be exerting an equal and opposite force upwards. And it's this force that we call the normal contact force. Now, non-cont forces don't have to be touching and so they can act through empty space. The three types you need to know are gravitational force, magnetic force, and electrostatic force. When we talk about these non-cont forces, we often talk about them as fields of influence around an object because the forces can act on anything in that surrounding area. For example, gravity is a force of attraction between any two objects that have mass like the Earth and you or me. But importantly, we'd still feel this force of attraction even if we weren't touching the Earth. Magnetic forces can be attractive or repulsive depending on the poles of the magnets and I'll cover this in another video. Finally, electrostatic forces which are between charged objects can also be attractive or repulsive and again I'll cover in another video. For all of these non-cont forces though, the strength of the force will decrease as the objects get further apart. If you haven't heard yet, you can find all of our videos on our website, cognito.org. You'll also find questions, flashcards, exam style questions, and pass papers. And we track all of your progress so that you always know what to study next. So sign up for free by clicking here or browse our playlist here on YouTube.