When does the speed of a ball thrown in the air start decreasing?

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In summary, when throwing a ball up vertically with no horizontal component, the speed of the ball starts decreasing as soon as it leaves your hand due to constant acceleration of gravity. The fastest speed the ball can achieve is the initial speed it was launched with, but this is only true if the ball is caught. In exam questions, where air resistance is assumed to be zero, the launch speed will be equal to the speed of the ball at the instant it hits your hand. However, in real life, air resistance will reduce the speed of the ball on its way down. To stop getting emails for a thread, click on "Thread Tools" and then "Unsubscribe from this Thread" on the secondary menu-bar at the top of the
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influx
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When you throw a ball up (vertically; with no horizontal component), when does the speed of the ball start decreasing? I mean it has to decrease for it to stop (momentarily) and then come back down.. Does the speed start decreasing as soon as the ball leaves your hand? or is it at another stage during the journey?
 
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welcome to pf!

hi influx! welcome to pf! :smile:
influx said:
When you throw a ball up (vertically; with no horizontal component), when does the speed of the ball start decreasing?


as soon as it leaves your hand …

its constant acceleration is g downward the whole time it's in the air …

if it starts with speed v upward, then after time t its speed is v - gt (ie downward after t = v/g) :wink:
 
  • #3


tiny-tim said:
..

Thanks :)

So the fastest speed the ball can achieve is the initial speed (the speed you launch the ball with)?

Also, on the journey back down, the speed of the ball at the instant it hits your hand (assuming you have not moved your hand since the launch) has to be less than the launch speed right? Is this due to the work done against air resistance?

Thanks :P
 
  • #4
influx said:
Thanks :)

So the fastest speed the ball can achieve is the initial speed (the speed you launch the ball with)?

only if you catch it! :biggrin:
Also, on the journey back down, the speed of the ball at the instant it hits your hand (assuming you have not moved your hand since the launch) has to be less than the launch speed right? Is this due to the work done against air resistance?

erm :redface: … in exam questions, there's never any air resistance! :wink:

(but yes you're correct … in real life, air resistance reduces the energy, and so the speed on the way down will be less)
 
  • #5
Oh yeah true! Thanks :)

So in exam questions (where air resistance = 0), its safe to assume that the launch speed = the speed of the ball at the instant when it hits your hand?
 
  • #6
influx said:
So in exam questions (where air resistance = 0), its safe to assume that the launch speed = the speed of the ball at the instant when it hits your hand?

yup! :biggrin:

(for that reason, if you're asked to find the speed on landing of something thrown out of a window, it doesn't matter whether it was thrown up or down!)
 
  • #7
tiny-tim said:
yup! :biggrin:

(for that reason, if you're asked to find the speed on landing of something thrown out of a window, it doesn't matter whether it was thrown up or down!)

Thanks :). One non-physics related question, how do I stop getting emails every time someone posts in a thread I posted in?
 
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at the top of each thread there's a secondary menu-bar …

click "Thread Tools" and then "Unsubscribe from this Thread" :wink:​
 
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tiny-tim said:
at the top of each thread there's a secondary menu-bar …

click "Thread Tools" and then "Unsubscribe from this Thread" :wink:​

Thank you
 

FAQ: When does the speed of a ball thrown in the air start decreasing?

How does gravity affect a ball thrown in the air?

Gravity is a force that pulls objects towards the Earth's surface. When a ball is thrown in the air, gravity acts upon it, causing it to fall towards the ground. This is why a ball thrown upwards eventually comes back down.

How does air resistance impact a ball thrown in the air?

Air resistance, also known as drag, is a force that opposes the motion of an object through air. When a ball is thrown in the air, air resistance acts upon it, slowing it down. This is why a ball thrown upwards does not reach the same height as it was thrown from.

Why does a ball thrown at an angle travel further than a ball thrown straight up?

When a ball is thrown at an angle, it has both horizontal and vertical components of motion. This means it will travel further than a ball thrown straight up, which only has a vertical component of motion. The horizontal component allows the ball to cover more distance.

How does the force of the throw impact the height and distance the ball travels?

The force of the throw, also known as the initial velocity, directly impacts the height and distance the ball travels. The greater the force, the higher and further the ball will go. This is because the initial velocity determines the ball's speed and height reached before gravity and air resistance begin to act upon it.

Can a ball be thrown in the air without experiencing gravity or air resistance?

No, it is not possible for a ball to be thrown in the air without experiencing gravity or air resistance. These are fundamental forces that act upon all objects in motion. However, the effects of these forces can be minimized by throwing the ball in a vacuum or in an environment with very little air resistance.

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