wk 9: 5.3, 7.1, 16.1

The elastic properties of the arteries are essential for blood flow. Explain importance of this in terms of the characteristics of flow of blood (pulsating or continuous).

Blood flows from heart, moves through arteries to body. when heart pumps blood into arteries they stretch & relax due to their elastic nature, therefore elastic property is essential for blood flow.

A box is pulled a distance, d, across a floor by a force F, which makes an angle, θ, w/ the horizontal. If magnitude of the force increased and angle was decreased, work done by force would:

Both will increase the work

Tensile strength

Breaking stress that will cause permanent deformation or fracture of a material.

Explain why pregnant women often suffer from back strain late in their pregnancy.

Center of mass shifts due to additional weight, boys tries to counter shift which causes back pain.

Deformation

Change in shape due to application of a force

Useful work is the work done by an external system. T or F

F

Work is done on a locked door that remains closed while you try to pull it open. T or F

F

unit for work and energy

Joules (J)

Hooke's Law Equation

Stress of a solid is directly proportional to the strain applied to it.

The work done by a force is zero if the displacement is either zero or perpendicular to the force. T or F

T

The work done is positive if the force and displacement have the same direction, and negative if they have opposite direction. T or F

T

Work is done on an object as you drop it from the second floor of a building to the ground floor. T or F

T

Describe a situation in which a force is exerted for a long time but does no work. Explain.

The Earth revolving around the sun - force is perpendicular to the direction Earth is moving... no change in PE or KE as it revolves around the sun; a beam holds up a roof, no displacement so no work.

Stress

The ratio of force to area, 𝐹/𝐴, measured in N/m2.

What are you feeling when you feel your pulse? Measure your pulse rate for 10 s and for 1 min. Is there a factor of 6 difference?

The stretch & relax of arteries. Plus rate is measure of # of times heart pumps out or arteries stretch & relax in 1 min. pulse rate will be the same

Would you expect your height to be different depending upon the time of day? Why or why not?

Yes, in morning height is slightly more b/c extending & shrinking of spinal cord. during day due to continuous movement spinal cord shrinks

Restoring force

any force that always acts to pull a system back toward equilibrium

Oscillation

back & forth motion of an object between 2 points of deformation

If the force and displacement are not collinear, which formula is used for work? Answers: a. W = F·d sin(θ) b. W = m·g·d sin(θ) c. W = F·d cos(θ) d. W = F cos (θ)

c. W = F·d cos(θ)

The work done on/by a spring is proportional to a. the square-root of the spring's displacement b. the spring's displacement c. the spring's displacement-squared d. the inverse of the spring's displacement

c. the spring's displacement-squared

With conversion, which quantity does not represent a spring constant? a. 100 N/m b. 100 lbs/ft c. 100 kN/cm d. 100 kg/m

d. 100 kg/m

Shear deformation

deformation perpendicular to the original length of an object. where 𝑆 is the shear modulus and 𝐹 is the force applied perpendicular to 𝐿0 and parallel to the cross-sectional area 𝐴

Work

force in direction of motion x distance through which force acts.

Give an example of a situation in which there is a force and a displacement, but the force does no work. Explain why it does no work.

if person is moving w/ constant velocity carrying a heavy box then there is no work done b/c force is at right angle to the motion of the box.

elastic potential energy

potential energy stored as a result of deformation of an elastic object, such as the stretching of a spring

Strain

ratio of the change in length to length, Δ𝐿/𝐿0, (a unitless quantity). In other words, stress=Y x strain

force constant k

related to the rigidity (or stiffness) of a system—the larger the force constant, the greater the restoring force, and the stiffer the system. The units of k are newtons per meter (N/m).

Simplest oscillations occur when...

restoring force is directly proportional to displacement.

Work-energy theorem

the result, based on Newtons laws, that the net work done on an object is equal to its change in kinetic energy

Useful work

work done on an external system