Why do NBA players sometimes jump backwards when shooting a basketball?

In summary, the conversation discusses the concept of center of mass in relation to shooting a basketball. It is noted that when a kid has a running start, both he and the ball move forward after a shot, but the velocity of the center of mass remains the same. However, when the kid has no running start, the center of mass must also remain the same, causing the kid to move back as the ball moves forward. This is not always observed in real life, as professional basketball players often jump backwards when shooting to create distance from a blocker. The difference in landing spot is due to the mass and speed of the ball, as well as the jumping technique used.
  • #1
toesockshoe
265
2
Let's say a kid is playing basketball. He has a running start, jumps and while he is the air he shoots. There are no external forces at the time he shoots (disregard the minimal airdrag). If there are no external forces, shouldn't the center of mass after he shoots be the same as it was before he shoots? This wouldn't be true though becuase both the kid and ball move forward (because we say that he has a running start). My guess would be that the position of the center of mass doesn't necessary need to be the same, but the velocity HAS to be the same. Thus, although after the shot, both the boy and ball move forward, the velocity of the center of mass is the same as it was RIGHT before the kid shot the ball (because the kid moves forward slower but the ball forward faster). Is this correct?

Another question about center of mass:

Lets continue with the basketball example. This time let's say that the kid has NO running start. He jumps vertically and shoots. In this case the velocity of the mass and boy before he shoots is 0 (because he has no running start). Becuase the center of mass HAS to be the same as where it was before the kid shoots, the kid HAS to move back because the ball moves forward. This however does not happen in real life... because the kid usually comes back vertically down with no backwards displacement. Furthermore, if you watch professional NBA games, you can see that sometimes as basketball players shoot the ball when they jump, they go back very far. What causes this difference? When I shoot the ball with a jump, I come back vertically down, but when an NBA player shoots the ball, they displace backwards by a tremendous amount.
 
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  • #2
toesockshoe said:
Let's say a kid is playing basketball. He has a running start, jumps and while he is the air he shoots. There are no external forces at the time he shoots (disregard the minimal airdrag). If there are no external forces, shouldn't the center of mass after he shoots be the same as it was before he shoots? This wouldn't be true though becuase both the kid and ball move forward (because we say that he has a running start). My guess would be that the position of the center of mass doesn't necessary need to be the same, but the velocity HAS to be the same. Thus, although after the shot, both the boy and ball move forward, the velocity of the center of mass is the same as it was RIGHT before the kid shot the ball (because the kid moves forward slower but the ball forward faster). Is this correct?
Seems correct.
Another question about center of mass:

Lets continue with the basketball example. This time let's say that the kid has NO running start. He jumps vertically and shoots. In this case the velocity of the mass and boy before he shoots is 0 (because he has no running start). Becuase the center of mass HAS to be the same as where it was before the kid shoots, the kid HAS to move back because the ball moves forward. This however does not happen in real life... because the kid usually comes back vertically down with no backwards displacement. Furthermore, if you watch professional NBA games, you can see that sometimes as basketball players shoot the ball when they jump, they go back very far. What causes this difference? When I shoot the ball with a jump, I come back vertically down, but when an NBA player shoots the ball, they displace backwards by a tremendous amount.

You don't come back perfectly vertical, it just seems so because of the vast mass difference between the ball and yourself.
Let's say you weigh 160 lbs. This would make your mass 117 times that of the basket ball. We'll also say that you shoot the ball at a speed of 10 ft/sec. You jump to a height of 1 1/2 feet and release the ball at the top of the jump. Your backward motion will be 1/117 that of the basket ball or ~ 1 in/sec. It will take you ~ 1/4 sec to fall back to the floor from 1 1/2 feet, meaning you will land just about 1/4 in. from where you took off. And that is assuming that you jumped perfectly vertically, with no backward or forward motion at all ( not very likely). In order to see a measurable difference in your landing spot caused by throwing the ball, you are going to have to throw something a lot more massive, or throw the ball very very fast.
 
  • #3
As Janus said. Plus the NBA player jumps backwards to create space between the release point of the ball and a blocker.
 
  • #4
MrAnchovy said:
As Janus said. Plus the NBA player jumps backwards to create space between the release point of the ball and a blocker.
oh yeah... good point.
 

What is the center of mass?

The center of mass is the point at which the mass of an object is evenly distributed. It is the average location of all the mass in an object.

Why is the center of mass important?

The center of mass is important because it helps us understand how an object will move or behave when subject to external forces. It is also used in calculations for stability and balance.

How do you find the center of mass?

The center of mass can be found by locating the balance point of an object, which can be done by suspending the object or by using a plumb line. It can also be calculated mathematically using the masses and positions of individual parts of an object.

Can the center of mass be outside of an object?

Yes, the center of mass can be outside of an object if the object has an irregular shape or if there are multiple objects connected together. In this case, the center of mass may be located in empty space.

How does the center of mass affect an object's stability?

The lower the center of mass is in an object, the more stable it will be. This is because a lower center of mass means there is less potential for the object to topple over when acted upon by external forces.

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