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Kinesiology 2241A/B Lecture Notes - Lecture 9: Potential Energy, Centripetal Force, Centrifugal Force

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uwostudent70
4 Jan 2021
School
Western University
Department
Kinesiology
Course
Kinesiology 2241A/B
Professor
Thomas Richard Jenkyn

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Document Summary

Recall newton"s 3rd law from last class if a force is applied to an object, that object pushes back with the. This pair of forces are the action force and the reaction force they are equal in magnitude and opposite in same force direction. This means that they originate in our external environment and act on the body. The reaction forces that we have been talking about are the external forces. The action forces that we have been talking about are internal forces. Internal forces and external forces are related by newton"s 3rd law but you need something" to push. These arise from our muscular contractions applying force to our skeleton and causing limbs to move against! When you don"t have something to push against, you can"t accelerate your center of mass. Internal (muscle) forces do not change the body"s center of gravity.

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Related Questions

Two forces are acting on an object. Which of the following statements is correct?

(a)The object is in equilibrium if the net torque on the object is zero.
(b)The object is in equilibrium if the forces are equal in magnitude and opposite in direction.
(c)The object is in equilibrium if the net force and the net torque on the object are both zero.
(d)The object cannot be in equilibrium because more than one force acts on it.
(e) The object is in equilibrium if the forces act at the same point on the object.

Two forces are acting on an object. Which of the following statements is correct? (a) The object is in equilibrium if the forces are equal in magnitude and opposite in direction. (b) The object is in equilibrium if the net torque on the object is zero. (c) The object is in equilibrium if the forces act at the same point on the object. (d) The object is in equilibrium if the net force and the net torque on the object are both zero. (e) The object cannot be in equilibrium because more than one force acts on it.

A) A siring is tied to a book and pulled lightly as shown at right. The book remains in contact with the table and does not move. Draw a free-body diagram for the book. Label each of the forces exerted on the book as you were instructed in the tutorial Forces.

B) How do the forces exerted on the book, in this case, compare to the forces exerted on the book when the string is not present? List any forces that are the same (i.e., same type of force, same direction, and same magnitude) in both cases. Make a separate list of forces that change (or are not present) when the string is pulled.

C) Consider the following statement made by a student about a book at rest on a level table: "The two forces exerted on the book are the normal force directed up and the weight of the book directed down. These are equal and opposite to one another. By Newtons third law they are (action-reaction) force pair, so the normal force is always equal to the weight of the book." Do you agree with the student? Explain why you agree or disagree.

D) Consider a book on top of a level table while the book is being pressed straight down by a hand. In the space below, draw a free-body diagram for the book. Label the forces as you did in the tutorial Forces. How do the forces exerted on the book in this case compare to the forces exerted on the book when the hand is not pushing? List any forces that are the same (i.e., same type of force, same direction, and same magnitude) in both cases. Make a separate list of forces that change (or are not present) when the hand is pressing down on the book.

E) When the hand is pushing down on the book, is the magnitude of the weight equal to the magnitude of the normal force exerted by the table on the book? How can you tell?