Physics Chapter 5: Friction and Drag

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Questions and Answers

What does the change in length of a material depend on?

The compression applied only

The tension applied only

The original length, applied force, and cross-sectional area (correct)

The material's color and temperature

If a rod's applied force doubles while maintaining its original length, what happens to the change in length?

It doubles (correct)

It halves

It remains the same

It quadruples

In the equation for change in length, what role does Young’s modulus (Y) play?

It measures the material's resistance to elastic deformation (correct)

It determines the length of the material

It affects the color of the material

It influences the cross-sectional area

What happens to the elasticity of human organs as a person ages?

It decreases Signup and view all the answers

Given a steel cable with a diameter of 5.6 cm and a maximum tension of 3.0 x 10^6 N, what is the significance of the cross-sectional area in tension calculations?

It inversely affects the change in length Signup and view all the answers

What is defined as the stress in a material?

The ratio of force to unit area Signup and view all the answers

If a material is subjected to tension and compression, what can be said about the change in length for small deformations?

The change in length is generally the same for both tension and compression Signup and view all the answers

When applying force to stretch a rod, what is the relationship between change in length (ΔL) and the original length (L0)?

ΔL is directly proportional to L0 Signup and view all the answers

What defines strain in terms of material deformation?

Change in length divided by the original length Signup and view all the answers

Which expression represents shear deformation?

∆x = F/(S*A) Signup and view all the answers

How does weight distribution affect the spinal column's curvature?

It increases the curvature and shear component of stress. Signup and view all the answers

Why is it more difficult to compress solids and liquids compared to gases?

Attractive forces in solids and liquids resist compression. Signup and view all the answers

What is bulk modulus in relation to volume change?

The ratio of volume change to pressure applied Signup and view all the answers

In which situation is the compressive force primarily due to weight?

Deep ocean pressures on marine structures Signup and view all the answers

When calculating the maximum horizontal force that can be applied without moving an object, which force is primarily considered?

Static friction Signup and view all the answers

What happens to stress in the spine when an individual adjusts their posture to maintain balance?

It increases due to higher shear forces. Signup and view all the answers

At terminal velocity, what must be true about the forces acting on the falling object?

The net force is zero. Signup and view all the answers

How is the drag force affected when an object is very small or moving slowly?

It is proportional to the object's velocity. Signup and view all the answers

What does Hooke's law state about small deformations and the force applied?

The deformation is linear and proportional to the force. Signup and view all the answers

In the context of drag force, which equation correctly expresses the balance of forces for an object at terminal velocity?

$𝑚𝑔 = 𝐹𝑑$ Signup and view all the answers

What characterizes the elastic behavior of materials as outlined by Hooke's law?

The material's original shape is restored once the force is removed. Signup and view all the answers

Which statement correctly describes tensile strength in materials?

It refers to the maximum stress a material can withstand before permanent deformation. Signup and view all the answers

What is the correct expression for the drag force experienced by an object falling through air at terminal velocity?

$𝐹_d = \frac{1}{2} C \rho A v^2$ Signup and view all the answers

Which of the following best describes the effects of viscosity on drag force as per Stokes' law?

Higher viscosity increases the drag force on the object in a fluid. Signup and view all the answers

Study Notes

Chapter 5: Friction, Drag, and Elasticity

Friction: A force that opposes motion between surfaces in contact. It permits movement.
Friction is parallel to the contact surface and acts in a direction opposing motion or attempted motion.
Kinetic friction: Friction between surfaces in relative motion. For instance, a hockey puck sliding on ice.
Static friction: Friction between stationary surfaces. Static friction is typically greater than kinetic friction.
The harder surfaces are pressed together, the greater the friction force required to move them.
Adhesive forces between surface molecules contribute to friction.
Objects in motion have fewer contact points, thus requiring a reduced friction force to maintain movement.

Drag Forces

Drag force: A force that opposes motion in a fluid (either liquid or gas)
Experienced when moving a hand through water; the faster the movement, the greater the force.
Drag, like friction, always opposes motion.
Unlike friction, the drag is proportional to a function of the object's velocity in the fluid.
Drag force depends on shape, size, velocity, and the fluid itself.
For bigger objects (cars, bicyclists, baseballs) not moving slowly, the drag force is proportional to the square of speed.
Mathematically, drag force (FD) is expressed as: FD = 1/2 * C * ρ * A * v²
- C = drag coefficient
- ρ = density of the fluid
- A = area of the object facing the fluid
- v = velocity of the object
Drag forces can impact a moving object's terminal velocity, the point where the net force becomes zero.

Elasticity: Stress and Strain

Deformation: Change in an object's shape due to force application.
Small deformations: Objects return to original shapes when force is removed (elastic deformation).
Hooke's Law: For small deformations, the amount of deformation is proportional to the force applied (F = k * ΔL).
- ΔL = change in length
- k = proportionality constant depending on shape/composition and force direction
Stress: Ratio of force to unit area (F/A).
Strain: Ratio of change in length to original length (ΔL/L₀).
For small deformations, stress is proportional to strain. -Stress = Y *Strain
Elastic Modulus (Young's Modulus): A material property that relates stress to strain in tension or compression (Y).
For metals, springs and other structures, the elastic region to satisfy Hooke's law is larger than in brittle materials like bones.
In materials like bones, the elastic region is small and fracture abrupt.
The breaking stress that leads to permanent deformation or fracture is the tensile strength.

Shear Modulus

Shear deformation involves perpendicular forces, rather than parallel forces as in tension/compression.
Similar to tension/compression concerning their proportional relationship to deformation, the equation for this force is, Shear Deformation (Δx)= (1/S)*(F/A)*Length(L₀) where S is the Shear Modulus.

Changes in Volume: Bulk Modulus

Solids and liquids are difficult to compress compared to gases.
Strong electromagnetic forces in solids and liquids resist compression.
Change in volume (ΔV) is related to the force (F), original volume (V₀), and bulk modulus (B) as: Change In Volume (ΔV) = (-1/B)*(F/A)*Volume(V₀)
A practical application of this principle is the creation of industrial-grade diamonds via high-pressure compression.

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Explore the concepts of friction, drag, and elasticity in this quiz based on Chapter 5 of your physics textbook. Learn about the differences between kinetic and static friction, as well as how drag forces operate in fluids. Test your understanding of these fundamental principles of physics.