# Each action there is a responsive reaction

• Werg22
In summary, the conversation discusses the concept of action and reaction, specifically in the case of a falling ball. It is mentioned that the ball is reflected in the opposite direction when it hits the ground, but there is a point where it drops to a velocity of zero before being reaccelerated. The group discusses the logic behind this phenomenon and talks about the factors that can affect it, such as friction, elasticity, and thermal energy. There is also a discussion about the force and time involved in reaccelerating the ball, with some equations being brought up. Overall, the conversation delves into the complexities of forces and motion in relation to a falling ball.
Werg22
We all know that to each action there is a responsive reaction. Let's take the case of a falling ball. Ignoring factors such as friction, elasticity and thermal energy, the ball is dropped from a certain distance perpendicularly above the ground with an inexistent initial velocity. At the instant the ball hits the ground with a certain a certain force, the ground applies an equal force on the ball. The ball is then reflected in the opposite direction. But to get from a direction to one that is opposite, the ball has to, at a certain point drop to a velocity of zero. My thoughts were, naturally, that the reaction force reaccelerates the ball until a certain velocity is reached (witch is equivalent to the final velocity of the falling motion). And here is my problem; if really this is the case, then the force needs a certain time to reaccelerate the ball. Since the force is equivalent to the one of gm, so the time needed would be the same as the time the ball was in the air… this is obviously wrong, but by what logic?

Werg22 said:
Since the force is equivalent to the one of gm, so the time needed would be the same as the time the ball was in the air… this is obviously wrong, but by what logic?
What makes you think the force equals the weight? It's much greater than that (at least for ball hitting a hard surface).

Okay, so the acceleration would be relative to the mass of the floor... thank you for teaching me!

That is not what Doc Al ment. Hardness $\neq$ Mass. Typical harder the surface the less energy lost from the ball and its return bounce.

This i know, but I am talking about the force, and ignoring such factors... Wouldnt the time the ball stays on the ground (then again ignoring all other factors) would be:
T= 2vm/F? Correct me if I am still wrong...

The time the ball spends on the ground depends on how the ground and ball deform.

In the ideal case where the ball and the ground do not deform then the ball spends zero time on the ground.

Your equation only works if the force provided by deformation is a constant this will not typically be true.
$$\int_{t_o}^{t_f}\vec{F}dt = 2\vec{v} m$$

Hummm I would be lying if I said I completely understand... thanks for helping, Ill investigate this.

## What is meant by "Each action there is a responsive reaction"?

"Each action there is a responsive reaction" is a scientific principle, also known as Newton's third law of motion. It states that for every action, there is an equal and opposite reaction.

## How does Newton's third law of motion apply to everyday life?

This law can be observed in many everyday situations, such as when we push against a wall and feel the wall pushing back with equal force. It also applies to the movement of objects, as seen in the recoil of a gun after firing a bullet.

## What is an example of an equal and opposite reaction?

An example of an equal and opposite reaction is the recoil of a gun. When a bullet is fired, the gun experiences a recoil in the opposite direction with the same amount of force.

## Does Newton's third law of motion apply to all types of forces?

Yes, Newton's third law of motion applies to all types of forces, including gravitational, frictional, and normal forces.

## How does Newton's third law of motion relate to the conservation of momentum?

Newton's third law of motion is closely related to the law of conservation of momentum, which states that the total momentum of a system remains constant in the absence of external forces. This is because the equal and opposite reactions in an action-reaction pair cancel each other out, resulting in no change in overall momentum.

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