Consider the propulsion of a fish through the water. A fish uses its fins to push water backwards. But a push on the water will only serve to accelerate the water. Since forces result from mutual interactions, the water must also be pushing the fish forwards, propelling the fish through the water. The size of the force on the water equals the size of the force on the fish; the direction of the force on the water backwards is opposite the direction of the force on the fish forwards.
For every action, there is an equal in size and opposite in direction reaction force. Action-reaction force pairs make it possible for fish to swim. Consider the flying motion of birds. A bird flies by use of its wings. The wings of a bird push air downwards. Since forces result from mutual interactions, the air must also be pushing the bird upwards.
The size of the force on the air equals the size of the force on the bird; the direction of the force on the air downwards is opposite the direction of the force on the bird upwards. For every action, there is an equal in size and opposite in direction reaction. Action-reaction force pairs make it possible for birds to fly. Consider the motion of a car on the way to school. A car is equipped with wheels that spin. As the wheels spin, they grip the road and push the road backwards.
Since forces result from mutual interactions, the road must also be pushing the wheels forward. Opposite magnetic poles N-S or S-N attract each other:. Like magnetic poles N-N or S-S repel each other:. An electrostatic force is experienced by any charged particle in an electric field.
Contact forces are forces that act between two objects that are physically touching each other. Examples of contact forces include:.
An object at rest on a surface experiences a normal contact force. For example, a book on a table. This activity is all about explaining using sketches. The focus should be on changes in motion and inertia. Other resources on Force Force Forces and Motion. Force Forces and Motion. Misconceptions Forces and Motion Many students do not see forces as arising from an interaction between two objects Number of Resources 4 Number of References 5 Number of Diagnostic Resources 1.
Forces and Motion Many students are unable to identify correctly the forces acting on each object in a situation where two or more objects interact Number of Resources 2 Number of References 3 Number of Diagnostic Resources 1. Forces and Motion Many students think of a force as a property of objects, not as something that arises when two objects interact Number of Resources 3 Number of References 16 Number of Diagnostic Resources 3. We've won an award!
Learn more. Close Physics Links Explorer Explore the links between different physics concepts. For simplicity sake, all forces interactions between objects can be placed into two broad categories:. Contact forces are those types of forces that result when the two interacting objects are perceived to be physically contacting each other. Examples of contact forces include frictional forces, tensional forces, normal forces, air resistance forces, and applied forces.
These specific forces will be discussed in more detail later in Lesson 2 as well as in other lessons. Action-at-a-distance forces are those types of forces that result even when the two interacting objects are not in physical contact with each other, yet are able to exert a push or pull despite their physical separation. Examples of action-at-a-distance forces include gravitational forces.
For example, the sun and planets exert a gravitational pull on each other despite their large spatial separation. Even when your feet leave the earth and you are no longer in physical contact with the earth, there is a gravitational pull between you and the Earth.
Electric forces are action-at-a-distance forces. For example, the protons in the nucleus of an atom and the electrons outside the nucleus experience an electrical pull towards each other despite their small spatial separation.
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