Ch.13 pt 2

Question 1

What refers to the point around which the mass and weight of a body are balanced, no matter how the body is positioned?

Answer 1

center of gravity

Question 2

The center of gravity of a perfectly symmetrical object of homogeneous density is __.

Answer 2

at the exact center of the object

Question 3

Mechanically, a body behaves as though all of its mass were concentrated __

Answer 3

at its center of gravity

Question 4

What do athletes in sports like long jump, high jump, and pole vault do in order to increase takeoff impulse?

Answer 4

lower their center of gravity prior to takeoff

Question 5

What is a reaction board?

Answer 5

specifically constructed device that uses a scale and a platform for determining the center of gravity location of a body positioned on top of it

Question 6

The center of gravity of a body is the point about which the sum of torques produced by all weights of the body segments is __

Answer 6

zero

Question 7

What is the segmental method?

Answer 7

procedure for determining the total body center of mass location based on the masses and center of mass locations of the individual body segments

Question 8

When mass distribution within an object is not constant, its center of gravity shifts __

Answer 8

in the direction of greater mass

Question 9

know the 2 formulas that determine a persons center of gravity location using the segmental method

Question 10

When a weight vector is drawn for an object displayed in a free body diagram, it acts __

Answer 10

at the center of gravity

Question 11

High jumpers, long jumpers, and pole vaulters lower their centers of gravity prior to takeoff, which enables them to lengthen the vertical path over which their bodies are accelerated during takeoff, thus facilitating a(n) ______.

Answer 11

high vertical velocity at takeoff

Question 12

What 3 forces create torques at the platform support in a reaction board?

Answer 12

• the weight of the board
• the weight of a person standing on the board
• the reaction force of the scale on the platform

Question 13

What has a larger influence on total-body center of gravity than many other factors, in the segmental method of determining a persons center of gravity location?

Answer 13

massive body segments

Question 14

How is the total-body center of gravity (CG) determined by the segmental method?

Answer 14

products of each body segment’s CG location and its mass are summed and then divided by the sum of all segmental masses

Question 15

What is an individual’s ability to control equilibrium?

Answer 15

balance

Question 16

What refers to the area bound by the outermost regions of contact between a body and support surface(s)?

Answer 16

base of support

Question 17

What’s 3 factors increase the ability of a body to maintain equilibrium?

Answer 17

• increasing friction between the body and the surfaces contact4ed
• vertically positioning the center of gravity as low as possible
• increasing the size of the base of support in the direction of the line of action of an external force

Question 18

How is stability is defined mechanically?

Answer 18

resistance to disruption of equilibrium

Question 19

What happens when the line of action of a body’s weight moves outside the base of support, creating a torque that tends to cause angular motion of the body?

Answer 19

disruption of stability

Question 20

Horizontally positioning the center of gravity of a body near the edge of its base of support on the side of an oncoming external force __

Answer 20

increases the body’s ability to maintain equilibrium

Question 21

What 2 factors affect a body’s stability?

Answer 21

• increasing amount of friction
• increasing body mass

Question 22

To achieve a state of static equilibrium, what conditions must be true?

Answer 22

• ΣT=0
• ΣFy=0
• ΣFx=0