# Why does a ball continue to travel upwards when thrown into the air?

• tyneoh
In summary, when a ball is thrown upwards, it will initially accelerate upwards while in contact with the hand, but upon release, the acceleration drops to -g and the ball will continue to move upwards with a decreasing velocity. The only force acting on the ball is gravity, which causes it to eventually come back down. The initial thrust from the hand is not present once the ball is released.
tyneoh
Hello everyone, I am have some confusion regarding gravity and a ball traveling upwards.

Suppose you throw a ball upwards into the air. At the beginning, the ball is at rest atop your hand, Freaction=mg. When your hand moves upwards to throw the ball, Freaction>mg and the ball accelerates upwards with acceleration a,while in contact with your hand. Upon release, the ball will travel upwards with the same acceleration.

But with the increase in height, a will decrease. I know that this is due to the pull of gravity but I can't seem to understand fully as when the ball soars, the upward thrust is greater than that of the weight of the ball, mg.

Thus if the thrust is greater than the pull of gravity on the ball, there is a net force acting upwards, propelling the ball skywards perpetually, which is illogical.

Could somebody please correct my reasoning and end my confusion? Many thanks in advance :)

tyneoh said:
When your hand moves upwards to throw the ball, Freaction>mg and the ball accelerates upwards with acceleration a,while in contact with your hand. Upon release, the ball will travel upwards with the same acceleration.
No. Upon release, the acceleration of the ball drops to -g.

tyneoh said:
But with the increase in height, a will decrease.
No, the velocity v will decrease. The acceleration during flight is constant -g (ignoring drag)

tyneoh said:
Thus if the thrust is greater than the pull of gravity on the ball,
There is no thrust once the ball leaves the hand. Just gravity.

A.T. said:
No. Upon release, the acceleration of the ball drops to -g.

No, the velocity v will decrease. The acceleration during flight is constant -g (ignoring drag)

There is no thrust once the ball leaves the hand. Just gravity.

I am starting to see your point here, but allow me to ask: when the ball leaves the hand, it will still travel upwards, right? Shouldn't the be a upward force compelling it to move?

tyneoh said:
I am starting to see your point here, but allow me to ask: when the ball leaves the hand, it will still travel upwards, right? Shouldn't the be a upward force compelling it to move?

No. In the absence of force the ball will continue to move at the same speed, in the same direction, forever. This principal is called momentum. Once the ball leaves your hand the only force acting on it is gravity, which is why it comes down. If not for gravity it would continue upward into the universe forever

All this assumes no air resistance.

tyneoh said:
I am starting to see your point here, but allow me to ask: when the ball leaves the hand, it will still travel upwards, right?
Sure, since it has an initial upward velocity.
Shouldn't the be a upward force compelling it to move?
No. In the absence of force, things keep moving at the same velocity. (Newton's 1st law.) Force is needed to change velocity, not maintain it. Once it leaves your hand, the only force acting on the ball is gravity, which accelerates the ball downward.

## 1. What is gravity?

Gravity is a fundamental force of the universe that causes objects with mass to be attracted to each other. It is responsible for keeping planets in orbit around the sun and objects on Earth from floating away into space.

## 2. How does gravity affect upward motion?

Gravity acts as a downward force on objects in motion, including those moving upward. This means that gravity can slow down or even stop the upward motion of an object, eventually causing it to fall back down to the ground.

## 3. Can an object go against the force of gravity and move upwards?

Yes, an object can move upwards against the force of gravity if it has enough energy to overcome it. For example, rockets are able to launch into space by using powerful engines to propel them upwards with enough force to counteract the pull of gravity.

## 4. How does the strength of gravity change with distance?

The strength of gravity decreases as the distance between two objects increases. This is described by the inverse square law, which states that the force of gravity is inversely proportional to the square of the distance between two objects.

## 5. How does gravity affect different objects?

Gravity affects all objects with mass, regardless of their size or composition. However, the strength of gravity can vary depending on the mass and distance of the objects involved. For example, a small object like a marble will experience a much weaker gravitational force than a larger object like a planet.

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