An upward force against gravity

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For example,when I throw a ball upwards,I applied a force upwards against the gravitational force,how do we calculate the initial velocity of the ball

Gravity applies it's force all the time. But you apply a force for as long as you are still touching the ball. As soon as you let it go, it continues upwards with its initial velocity, that you have given it by accelerating it upwards, and trek only gravity works during the flight. So it slows down.

It all comes down to the total force that the object feels. Newton's 2nd law says this.

$$\sum F=ma$$

During the flight, it only feels gravity. So it only feels a force downwards. So it accelerates downwards. So it slows down.

During the throw while you are still in contact with the object, it feels gravity downwards but also you force upwards. If you force is largest, then it accelerates upwards. So it speeds up upwards. Which speed it then reaches at the end of your throw just before you don't touch it any more, depends on for how long you applied your throwing force.

if the force applied is greater than the gravitational force on the first moment,how do I know the changes in the acceleration of the ball?

You know the acceleration from Newton's 2nd law above. You just have to know the throwing force which you are applying.

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Wen Wen Hoh
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Updated on January 04, 2023

Comments

  • Wen Wen Hoh
    Wen Wen Hoh 10 months

    If two forces are applied against each other,we can simply sove it by subtraction.But what if a force is constantly applied while the other is not?For example,when I throw a ball upwards,I applied a force upwards against the gravitational force,how do we calculate the initial velocity of the ball and if the force applied is greater than the gravitational force on the first moment,how do I know the changes in the acceleration of the ball?It would be best if you can provide me an example. (I have learnt the basic formula such as v^2=u^2+2as but most of them did not tell regarding this type of situation.)

    • QuIcKmAtHs
      QuIcKmAtHs almost 6 years
      The ball decelerates at -9.81ms^-2(upwards) and accelerates 9.81ms^-2(downwards)
    • Wen Wen Hoh
      Wen Wen Hoh almost 6 years
      If lets say my original upward force was 20 N and the mass of the ball is 0.5 kg,the initial upward acceleration would be 40 ms^-2 ,while the gravity acts 9.8 ms^-2 downwards,would the upward acceleration be decreasing at the rate of 9.8 every second?
    • QuIcKmAtHs
      QuIcKmAtHs almost 6 years
      The upwards speed decreases, not acceleration. In this case, let us assume air resistance is negligible so acceleration up is constant(or down)
    • Bill N
      Bill N almost 6 years
      Draw a free-body diagram showing the forces (NOT the anticipated accelerations). Once you have the net force, then you can calculate the acceleration. Gravity produces a force called weight, not an acceleration. Net force produces acceleration. Remember that forces are vectors and must be handled differently from mere numbers.
    • Bill N
      Bill N almost 6 years
      In your example in the comment, if the upward due to the hand is a constant 20 N, then the net upward vector components would be (if up is + direction) 20-mg= 20-0.5(9.8) N. That would be the $ma$ while in contact with your hand. After it leaves your hand, the net force would be -mg.
    • Wen Wen Hoh
      Wen Wen Hoh almost 6 years
      So the initial velocity would be (20-mg)/m?