Can You Calculate the Force of a Basketball Using Mass and Acceleration?

[Peter G.]

Say I threw a Basketball at a friend and I wanted to calculated the force it exerted on him, could I do the following? (from an introductory Physics point of view)

Use: F = m x a

1. Weigh the ball
2. Measure the distance between the ball and him, throw the ball and record the time it took for it to hit him: (E.x: He is standing at 10 m away from me, it took the ball 1 second to reach him, it accelerated at 10 m/s²
3. Then, multiply the mass by the acceleration for the Force at which the ball hits him?

Would that work? Thanks!

 

[PhanthomJay]

No. First off, the ball would not be accelerating horizonatlly after it was released from your hand..., if anything, it would be decelerating due to air resistance. But regardless, this has little to do with the force of the ball on him, except for its speed just before impact. But them to calculate the force of impact, you would need to know the time elapsed during impact ( probably just fraction of a second), or the amount of deformation during impact, and the rebound speed at the instant it leaves his body. These would be difficult to calculate. Assume the ball was thrown at 10m/s, rebounded back at 5 m/s, and all this took place during an impact time of 0.05 second , then the average force exerted would be equal to ma, where a is the deceleration of the ball during impact, a= {(-5) - 10}/ 0.05 = - 300m/s/s, and m is about 0.5 kg, so the average force of impact would be about 150 N, or about 30 pounds roughly. These are just rough numbers...if the ball was thrown faster and ir rebounded almost just as fast, and the collision time was shorter, the force could easily be 10 times or more greater than that.

 

[Peter G.]

Ah ok thanks. I never understand in which scenario I can use F = m x a

 

[PhanthomJay]

Well, you are using F_net =ma...but the 'a' is the acceleration during impact, not any acceleration before impact. Speaking of impact, what happens when an irresistable force meets an immovable object? Check out this video of a jet slamming at 500 mph into a concrete barrier..designed to test the the missile protection capabilities of a thick walled concrete reactor enclosure...we used to design them for telephone poles being hurled at the dome at 100 mph from a say tornado...or a vehicle at 30 mph...not any more

http://www.crazywebsite.com/Pg-Online-Funny-Videos/F-4-Nuke-Crash-Test-1.html