Estimate the average force that a major-league pitcher...

Name: Problem 31, Chapter 4: University Physics with Modern Physics
Uploaded: 2021-01-29T04:51:07-08:00
Duration: 4 min 24 s
Channel: Bianca Gualtieri
Description: Estimate the average force that a major-league pitcher exerts on the baseball when he throws a fastball. Express your answer in pounds. In your solution, list the quantities for which you estimate values and any assumptions you make. Do a web search to help determine the values you use in making your estimates.

Estimate the average force that a major-league pitcher exerts on the baseball when he throws a fastball. Express your answer in pounds. In your solution, list the quantities for which you estimate values and any assumptions you make. Do a web search to help determine the values you use in making your estimates.

Key Concepts

Unit Conversions

Unit conversions are necessary when the calculation initially yields a force in one unit (such as newtons) and needs to be expressed in another unit (such as pounds-force). Understanding the conversion factors between units is critical to accurately report the final result in the desired measurement system.

Estimation Techniques

Estimation techniques involve making reasonable assumptions and using approximate values for physical quantities such as ball mass, velocity, and contact time. These techniques are essential when precise measurements are unavailable, allowing one to derive an approximate value for the force that a pitcher exerts on the baseball.

Impulse and Momentum

Impulse is defined as the product of the average force applied and the time interval during which it is applied, and it equals the change in momentum of the object. This concept is crucial for estimating the force exerted on a baseball because it connects measurable or estimated values—such as the mass of the baseball, the speed attained by the pitch, and the time of contact—to determine the average force.

Newton's Second Law

Newton's Second Law is the principle that relates force to the rate of change of momentum. In the context of the problem, it forms the basis for estimating the force exerted during the ball’s acceleration by stating that the force is equal to the change in momentum divided by the time over which that change occurs.

Transcript

00:01 So for this problem, we have a baseball player throwing a ball.

00:07 So here we're going to have to make a bunch of assumptions and then do our math base off of that.

00:14 So we're going to assume the mass of the baseball is 145 grams, which is 0 .145 kilograms.

00:24 And remember that conversion is just converting grams to kilograms, which, 1 gram is equal to 10 to the negative 3 kilograms.

00:41 All right, so we're going to assume that the pitcher is going to throw a straight ball horizontally along the x direction, just to make things a little easier.

00:56 Now one besides this kinetic equation i wrote here, we also have to take into consideration new and second law, which is force equals mass times acceleration.

01:12 So how do we start this problem? so we have to, let's make an assumption about the time because we're not given a time.

01:21 So this time represents a time to throw the ball from the time the ball is.

01:26 In his hand to when he actually throws in.

01:30 So we are going to set t equal to say 0 .1 seconds.

01:35 So then we're going to assume average arm linked.

01:39 So why are we going to do this? so that is going to be the x minus x not difference.

01:45 So x not is the initial position, while x here is going to kind of act like the final position once the arm is extended.

01:58 So i just googled the length of an arm.

02:03 So that is 65 centimeters.

02:07 So the difference would be because the initial position we're going to have that equal to zero, and then x equals 0 .65 meters...

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