what are the action and reaction forces?
Gravity pulls the book down.
Gravity pulls the book down.
Gravity pulls down and friction pushes up.
Gravity pulls down and friction pushes up.
Gravity pushes the book up.
Gravity pushes the book up.
The book pushes down on the table and the table pushes up on the book.
The book pushes down on the table and the table pushes up on the book.
Skip to navigation
The action force in each scenario is the force being exerted by one object on another. The reaction force is the force exerted by the second object back on the first object, resulting in an equal and opposite force.
In the first example, the action force is gravity pulling the book down, and the reaction force is the book pushing up on gravity.
In the second example, gravity is still the action force pulling the book down, but the friction between the book and the surface it is resting on provides the reaction force pushing the book up.
In the third example, the action force is gravity pushing the book up, and the reaction force is the book pushing down on gravity.
In the final example, the action force is the book pushing down on the table, and the reaction force is the table pushing up on the book.
Action and reaction forces refer to a pair of forces that occur when two objects interact with each other. According to Newton's third law of motion, for every action, there is an equal and opposite reaction.
In the given examples, the action and reaction forces are as follows:
1. Gravity pulls the book down - The action force here is the gravitational pull exerted by the Earth on the book, causing it to move downwards. The reaction force is the equal and opposite force exerted by the book on the Earth.
2. Gravity pulls down and friction pushes up - Again, the action force is the gravitational pull exerted by the Earth on the book, causing it to move downwards. The reaction force is the equal and opposite force exerted by the book on the Earth. Additionally, the reaction force to the friction acting in the upward direction is the equal and opposite force exerted by the book on the surface it rests on.
3. Gravity pushes the book up - This scenario is not possible as gravity always acts downwards due to the gravitational pull of the Earth. So, there is no action and reaction force pair in this case.
4. The book pushes down on the table and the table pushes up on the book - Here, the action force is the downward force exerted by the book on the table. The reaction force is the equal and opposite force exerted by the table on the book, pushing it upwards.
Remember, the action and reaction forces always occur in pairs and have the same magnitude but act in opposite directions.
The concept of action and reaction forces is a fundamental principle in physics, also known as Newton's third law of motion. According to this law, for every action, there is an equal and opposite reaction.
In the case of the examples given:
1. When gravity pulls the book down, the action force is the force of gravity acting on the book, and the reaction force is the book exerting an equal and opposite force on the Earth (though the effect on the Earth is negligible due to its large mass).
2. When gravity pulls the book down and friction pushes up, the action force is still the force of gravity acting on the book, and the reaction force is the book exerting an equal and opposite force on the Earth. However, in addition to that, there is also a frictional force between the book and the surface it is resting on, which opposes the motion and pushes the book up. In this case, the frictional force acts as the reaction force to the force the book exerts on the surface.
3. When gravity pushes the book up, this is not possible as gravity always pulls objects towards the center of the Earth. So, this scenario does not follow Newton's third law.
4. When the book pushes down on the table and the table pushes up on the book, the action force is the force exerted by the book on the table, and the reaction force is the force exerted by the table on the book, in the opposite direction. This pair of forces follows Newton's third law, where the force exerted by the book is equal and opposite to the force exerted by the table.
It's important to note that action and reaction forces always occur in pairs and act on different objects. These pairs of forces are simultaneous and of equal magnitude but act in opposite directions.