Ch 8: Equilibrium and Elasticity Flashcards
An old-fashioned tire swing exerts a force on the branch and a torque about the point where the branch meets the trunk. If you hang the swing closer to the trunk, this will ________ the force and
________ the torque.
A. Increase, increase
B. Not change, increase
C. Not change, not change
D. Not change, decrease
E. Decrease, not change
F. Decrease, decrease
D. Not change, decrease
What are the two conditions required for static equilibrium of an extended object?
No net force.
No net torque.
p. 245
For an object in static equilibrium, the net torque about _____ point must be zero.
every
What function is sin/cos?
tangent
What function is cos/sin?
1/tan
(inverse tangent)
The spring-like bonds between the atoms in steel are quite stiff, but they can be stretched or compressed, meaning that even a steel rod is somewhat _______. For a 1.0 m long steel rod, 1.0 cm-diameter, it would take a force of 16,000 N to stretch the rod by only 1 mm, corresponding to a spring constant of 1.6 x 107 N/m.
elastic
p. 255
What is Young’s modulus?
a measure of elasticity (or compression), equal to the ratio of the stress acting on a substance to the strain produced.
It does not depend on shape or size of an object, only the material from which it is made.
From Britannica:
“Young’s modulus, numerical constant, named for the 18th-century English physician and physicist Thomas Young, that describes the elastic properties of a solid undergoing tension or compression in only one direction, as in the case of a metal rod that after being stretched or compressed lengthwise returns to its original length. Young’s modulus is a measure of the ability of a material to withstand changes in length when under lengthwise tension or compression.”
p. 255
What is the definition of stress?
In what units is it measured?
the ratio of force to cross-section area
N/m2
p. 255
What is the definition of strain?
the ratio of the change in length to the original length
p. 255
What equation related strain, stress, and Young’s modulus?
F/A = Y(ΔL/L)
F is force, A is area, Y is Young’s modulus, ΔL is the change in length, and L is the original length.
True or false:
Every solid object stretches, compresses, or deforms when a force acts on it.
TRUE
p. 252
If you stretch a rubber band, there is a force, known as a ________ force, that tries to pull the rubber band back to its equilibrium length. Systems that exhibit such restoring forces are called _______.
restoring
elastic
p. 252
The spring force always points in the direction opposite the displacement from equilibrium. The spring force is also proportional the displacement of the end of the spring. This is a linear relationship, and the slope k of the line is the __________ ________, described by the equation:
Fsp = k Δx
In other words, compressing or stretching a spring twice as far results in a restoring force that is twice as large.
proportionality constant
p. 252
In what units is k, the spring constant, measured in?
N/m
