# Newton’s third law

Newton’s third law states that when one object exerts a force on a second object, the second object simultaneously exerts a force of equal magnitude but in the opposite direction on the first object. This law implies that forces always occur in pairs, and the nature of the forces is such that they act on different objects. For example, when you push against a wall, the wall pushes back with an equal force. This principle of equal and opposite forces is a fundamental concept in physics and applies to various situations, from everyday interactions to complex systems. Newton’s third law is closely linked to the conservation of momentum, as the forces involved in interactions between objects can lead to changes in momentum while still maintaining overall momentum conservation in a closed system.

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## Examples

### Cannon

When a cannon fires a cannonball, Newton’s third law of motion comes into play. According to this law, every action force has an equal and opposite reaction force. The action force occurs when the hot gases produced by burning gunpowder propel the cannonball forward. At the same time, an equal and opposite reaction force is exerted on the cannon, pushing it backward. This reaction force, acting in the opposite direction to the expulsion of gases, results in a recoil or kickback of the cannon. The backward force on the cannon is a direct consequence of the forward force applied to the cannonball, showcasing the principle that every action has an equal and opposite reaction, as stated by Newton’s third law.

### Bird

Newton’s third law of motion states that for every action force, there is an equal and opposite reaction force. When a bird is flying, this law is evident. As the bird flaps its wings, it exerts a downward action force against the air. Simultaneously, the air exerts an equal and opposite reaction force on the wings of the bird, pushing them upward. This reaction force provides the necessary lift for the bird to stay airborne and counteracts the downward force of the wing flaps. Thus, the bird’s ability to fly is a direct result of the equal and opposite forces involved, which exemplifies Newton’s third law.

### Boat

When an individual jumps off a boat, Newton’s third law of motion comes into play. This law states that every action has an equal and opposite reaction. As the individual pushes against the boat with their legs to jump, they exert an action force that propels the boat backward. At the same time, according to Newton’s third law, the boat exerts an equal and opposite reaction force on the individual’s legs to propel them forward. These forces, with equal magnitudes but opposite directions, exemplify the principle of action and reaction. The individual’s ability to jump is a result of the interplay between these equal and opposite forces, as described by Newton’s third law.

### Fish

When a fish swims, Newton’s third law of motion is at work. The fish propels itself forward by exerting an action force on the water using its fins and tail, generating a push against the water. As stated by Newton’s third law, the water responds with an equal and opposite reaction force, pushing the fish backward. This reaction force from the water provides the necessary propulsion for the fish to swim. The fish’s ability to swim is made possible by the balanced interaction between the action force it exerts on the water and the equal and opposite reaction force exerted by the water on the fish. Thus, Newton’s third law demonstrates that for every action force, there is an equal and opposite reaction force, and exemplifies the principle that every action has an equal and opposite reaction.

### Gun

The firing of a gun provides a clear demonstration of Newton’s third law in action. When the trigger is pulled, the ignited gunpowder generates expanding gases that apply a forward action force on the bullet, and propels it out of the barrel. At the same time, in accordance with Newton’s third law, the bullet exerts an equal and opposite reaction force on the gun. This interaction between the bullet and the gun, as dictated by Newton’s third law, illustrates the fundamental principle that every action force has an equal and opposite reaction force.

### Spring

When a spring is pressed with a finger or hand, Newton’s third law is demonstrated. This law states that every action force has an equal and opposite reaction force. When force is applied to the spring, it compresses, and an action force is exerted. At the same time, the spring pushes back with an equal and opposite reaction force, creating resistance against the finger or hand. This balanced interplay between the action force and the reaction force exemplifies Newton’s third law, and emphasizes the principle that action and reaction forces are always equal and opposite.