[Music] hi and welcome back to free science lessons. co.uk by the end of this video you should be able to describe what's meant by a contact and a non-con force you should then be able to State examples of contact and non-con forces so we're going to start by looking at what's meant by a force I'm showing you the definition here a force is a push or a pull that acts on an object due to the interaction with another object all forces have got both magnitude in other words size and a Direction so that means that force is a vector quantity and the unit of force is the Newton now all forces can be divided into two categories these are contact forces and non-contact forces and you need to be able to identify these in your exam we're going to start by looking at contact forces remember that all forces take place when two objects interact and the case of contact forces the two objects are physically touching tension in a rope is an example of a contact force in the case of the tug of war this force of tension is pulling on the soldier another example of a contact force is friction I'm showing you here an airplane landing on the sea in this case the force of friction is acting between the water and the airlane this causes the airplane to slow down and come to a stop air resistance is another example of a contact force and we can show that with this sky diver as the sky diver falls through the air air particles collide with the parachute this causes the force of air resistance to act upwards okay the final contact force is called normal contact force and students sometimes find this idea a bit tricky I'm showing you here a lum on a table the lump is exerting a downward force on the table and that force is the weight of the lump we' be looking at weight in the next video at the same time the table is exerting an upward force on the lamp this is called the normal contact force and this force can only happen if the two objects are in direct contact don't worry too much about normal contact force we'll be seeing it again in a later video okay let's take a look now at non-con forces in the case of non-contact forces the two objects are physically separated and there are three examples gravitational force attracts all objects to other objects for example the gravitational force attracts the International Space Station to the Earth and the Earth to the International Space Station the second non-c contct force is electrostatic force this is the force between two charged objects we've already seen this in the video on electric Fields objects with opposite charges experience an electrostatic force of attraction like this whereas objects with the same type of charge experience an electrostatic force of repulsion and I'm shown that here in both cases the two objects are physically separated as the electrostatic force is a non-con force okay the last non-contact force is the magnetic force this is the force experienced by certain objects in a magnetic field and we're going to be looking at the magnetic force in more detail in later videos remember you'll find plenty of questions on contact and non-con forces in my vision workbook and you can get that by clicking on the link above [Music]