Kinesiology 2241A/B Chapter Notes -Buoyancy

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lavenderswan263

19 Apr 2013

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When a force is applied to an object, it moves the object"s c of g in a linear path. When the object is restricted to movement about an axis, the force causes the object to rotate: except when the force is applied directly at the axis of rotation. Eccentric force off-center force that causes torque. Four properties of torque-producing forces: magnitude, direction, line of action, point of application. Torque is produced by muscles when they pull on bones, and the result is rotary motion of the body segments about an axis. The stronger the muscle contraction, the greater torque on the bone. The longer the force arm, the greater the torque. Teeter-totter: if the weight is less (ie. a child), it creates less torque, if the weight is placed closer to the axis it creates less torque. If many torques are applied to a system, the sum of the torques tells the movement direction (net torque)

Related Questions

The tangential force method involves finding the component of the applied force that is perpendicular to the displacement from the pivot point to where the force is applied. This perpendicular component of the force is called the tangential force.

(a) What is , the magnitude of the tangential force that acts on the pole due to the tension in the rope?

Express your answer in terms of

and

.

When using the tangential force method, you calculate the torque using the equation

$\tau = f_{\rm t} d$ ,

where

is the distance from the pivot to the point where the force is applied. The sign of the torque can be determined by checking which direction the tangential force would tend to cause the pole to rotate (where counterclockwise rotation implies positive torque).

(b) What is the magnitude of the torque

on the pole, about point A, due to the tension in the rope?

Express your answer in terms of

, and

The moment arm method involves finding the effective moment arm of the force. To do this, imagine a line parallel to the force, running through the point at which the force is applied, and extending off to infinity in either direction. You may shift the force vector anywhere you like along this line without changing the torque, provided you do not change the direction of the force vector as you shift it. It is generally most convenient to shift the force vector to a point where the displacement from it to the desired pivot point is perpendicular to its direction. This displacement is called the moment arm.

For example, consider the force due to tension acting on the pole. Shift the force vector to the left, so that it acts at a point directly above point A in the figure. The moment arm of the force is the distance between the pivot and the tail of the shifted force vector. The magnitude of the torque about the pivot is the product of the moment arm and force, and the sign of the torque is again determined by the sense of the rotation of the pole it would cause.

, the length of the moment arm of the force.

Express your answer in terms of

and

(d)Now consider a woman standing on the ball of her foot as shown. A normal force of magnitude

acts upward on the ball of her foot. Achilles' tendon is attached to the back of the foot. The tendon pulls on the small bone in the rear of the foot with a force

. This small bone has a length

, and the angle between this bone and the Achilles' tendon is

. The horizontal displacement between the ball of the foot and the point P is

Find τp, the torque about point P due to the force applied by the Achilles' tendon. Express your answer in terms of F, ϕ, and x.

byzantiumarmadillo929

Express your answer in terms of

and

.

When using the tangential force method, you calculate the torque using the equation

$\tau = f_{\rm t} d$ ,

where

on the pole, about point A, due to the tension in the rope?

Express your answer in terms of

, and

, the length of the moment arm of the force.

Express your answer in terms of

and

(d)Now consider a woman standing on the ball of her foot as shown. A normal force of magnitude

acts upward on the ball of her foot. Achilles' tendon is attached to the back of the foot. The tendon pulls on the small bone in the rear of the foot with a force

. This small bone has a length

, and the angle between this bone and the Achilles' tendon is

. The horizontal displacement between the ball of the foot and the point P is

Find τp, the torque about point P due to the force applied by the Achilles' tendon. Express your answer in terms of F, ϕ, and x.

turquoiseworm20

What is the difference between the study of kinematics and kinetics in regard to forces?

What three components that make up the musculoskeletal âsystemâ.

The musculoskeletal system is composed if many simple machines. There are 4 potential uses for these simple machines, list 2 of these uses.

Fill in the blank a _________ is used to alter the resulting direction of the applied force.

In the body what component acts as a lever and what acts as the axis?

When we think of a lever set up, what does FAR refer to?

Draw a basic F.A.R for each of the following and give an example of where in the body you may find each.

First class lever:

Second class lever:

Third class lever:

Which class of levers is designed best for speed and range of motion and which is best for strength?

What forces determine amount of torque in a system?

A. How much torque needs to be produced to move 60 kg (R) when the RA is 0.30 m and the FA is 0.1 meters?

b. What value could you change to decrease the torque needed to lift the SAME object.

c. Draw the F.A.R unit (say an arm lifting a bucket) label the elements and explain why what you changed in b would decrease torque needed.

12. a. What is the âcontractileâ unit of muscle called? ______________

b. what is the non-contractile element (series elastic element) in a muscle lever system?

13. in regards to âpowerâ which is more powerful, muscle fibers arranged in Parallel or bipennate muscles? ___________

Why?

14. When weight lifting with the goal of increasing strength, what physical characteristic of the muscle are you changing to bring about that increased strength? __________________

15. What is the branch of FDA that controls regulation of medical devices? ____________

16. Which of the following statements is false?

A device can be an instrument or an apparatus.

A device can be something used to diagnose a disease

A device can change the chemistry of your cells

A device can be something that delivers a drug to your body

17. Give one example of a..

Class I device

Class II device

Class III device

18. Which of the following is true regarding device classification?

Devices with the least risk to the patient are considered Class III

A class III device has a high risk potential to the patient

Class III devices are the easiest to get approved

Testing devices on humans is easy and follows no specific guidelines

19. Explain the difference between Harm and Risk.

20. What is a âsubstantial equivalentâ? Is it easier or harder to get approval for a Device that has an SE?

21. Which of the following would not be a priority when developing a medical device?

Cost

Ergonomics

Ease of sterilization

Material

None of the above

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Kinesiology 2241A/B Chapter Notes -Buoyancy

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