To throw a ball, do you exert an impulse on it? Do you exert...

Name: Problem 80, Chapter 3: Conceptual Physical Science
Uploaded: 2019-08-16T22:20:24-08:00
Duration: 8 min 43 s
Channel: Andre Felipeti
Description: To throw a ball, do you exert an impulse on it? Do you exert an impulse to catch it if it's traveling at the same speed? About how much impulse do you exert, in comparison, if you catch it and immediately throw it back again? (Imagine yourself on a skateboard.)

To throw a ball, do you exert an impulse on it? Do you exert an impulse to catch it if it's traveling at the same speed? About how much impulse do you exert, in comparison, if you catch it and immediately throw it back again? (Imagine yourself on a skateboard.)

Key Concepts

Impulse

Impulse refers to the product of force and the time interval over which it acts. It is a vector quantity that, when applied to an object, changes the object's momentum. Impulse is fundamental in describing how forces, applied over finite durations, affect the motion of objects.

Momentum

Momentum is the measure of an object's motion and is defined as the product of its mass and velocity. This quantity is conserved in isolated systems, meaning that any change in momentum in one part of the system must be balanced by changes elsewhere. Understanding momentum is crucial for analyzing interactions involving motion.

Impulse-Momentum Theorem

The impulse-momentum theorem establishes that the impulse applied to an object is equal to the change in its momentum. This theorem provides a clear link between the force applied over a period of time and the resulting change in an object's state of motion. It is useful in quantifying how actions like accelerating, stopping, or reversing an object's motion affect its momentum.

Reversal of Momentum

When an object’s direction is reversed, the change in momentum is effectively the sum of the magnitude of its initial momentum and the magnitude needed to bring it to the same speed in the opposite direction. This concept is important in scenarios where an object is caught and then thrown back, as the impulse required to change its direction involves not only stopping it but also reaccelerating it in the opposite direction.

Transcript

00:01 If you catch a ball at a certain speed, do exert impulse in it? and if you throw at the same speed, do you also exert impulse in it? and how does it compare it if you catch a ball and then immediately throw it back away? so to think of this, let's put the situations here.

00:22 We have the ball and the person's hand.

00:27 And then once you catch the ball, then you have the person's hand.

00:35 And the ball comes to a rest.

00:40 In the initial case, we're going to have the hand is at rest.

00:45 So momentum, initial for a, let's call this a, which is going to be the mass of the ball, times the velocity of the ball.

01:08 And let's call to the right positive.

01:13 It and then momentum final the ball is at rest the hand is at rest there's zero velocity everywhere so momentum final is zero then for the second case it is throwing the ball so initially you had the ball in your hands and then you throw that ball at a speed v so the momentum initial is going to be zero because both the head and the ball are at rest and then the momentum final for the ball.

02:27 We're going to have the mass of the ball, which again, it's m times the velocity of the ball, which if we take in account the direction, becomes minus mv.

02:43 This one would be positive mv since it's going to the positive side.

02:49 And then in situation c, we have initially the ball coming at velocity v towards your hand, and then you're going to catch it.

03:17 And then after you catch it, you're going to throw it back with the same velocity v.

03:31 So the pretty thing about momentum is that we only care about the changing the momentum from before and after.

03:41 Say that this is immediate it takes almost zero seconds between throwing, catching and throwing it back...

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