Physics Work and Friction Concepts

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Questions and Answers

What causes weight to vary from one celestial body to another?

The distance from the Sun

The mass of the object

The object's speed in space

The gravitational force acting on that body (correct)

Which statement is true regarding inertia?

Inertia decreases with increasing mass

Inertia is not related to motion or rest

Inertia only applies to moving objects

Inertia is the resistance to change in motion (correct)

How is work defined in physics?

Work is energy stored in an object

Work can occur without any movement of the object

Work is the mass of an object multiplied by its speed

Work is done when a force moves an object through a distance (correct)

What is the formula used to calculate work done?

W = Fs Signup and view all the answers

If a force of 50 newtons moves an object 5 meters, how much work is done?

250 joules Signup and view all the answers

What unit is used to measure power in the SI system?

Watt Signup and view all the answers

When climbing stairs, what influences the amount of power used?

The speed at which they climb Signup and view all the answers

What occurs when no distance is moved while a force is applied?

Work done is zero Signup and view all the answers

What is the effect of lubrication on friction?

Minimizes unwanted friction Signup and view all the answers

Which combination of materials has the highest coefficient of friction?

Rubber tyre on a dry runway Signup and view all the answers

What type of friction is experienced when a vehicle starts moving from rest?

Static friction Signup and view all the answers

How is the sliding friction force calculated?

F = μN, where N is the weight of the object Signup and view all the answers

When pulling a box at a slight upward angle, why is it easier compared to pushing it?

It reduces the effect of friction Signup and view all the answers

What happens to friction when lift is reduced in an aircraft?

Friction increases, allowing for early braking Signup and view all the answers

What is a characteristic of rolling friction compared to sliding friction?

Rolling friction has less resistance than sliding friction Signup and view all the answers

Which of the following coefficients of friction indicates the least resistance?

Teflon on Teflon (0.04) Signup and view all the answers

What is the equivalent of one horsepower in foot-pounds per second?

550 foot-pounds per second Signup and view all the answers

How can power be expressed mathematically using force and velocity?

P = Fv Signup and view all the answers

What does the force of gravity cause unsupported objects to do on Earth?

Fall towards the center of the Earth Signup and view all the answers

What does the law of Conservation of Energy state?

Energy can neither be created nor destroyed. Signup and view all the answers

What type of energy is stored in a body due to its position or condition?

Potential energy Signup and view all the answers

Which of the following correctly expresses the relationship between weight (W), mass (m), and acceleration due to gravity (g)?

W = mg Signup and view all the answers

How is kinetic energy calculated?

KE = ½ mv² Signup and view all the answers

What is the value of acceleration due to gravity on Earth, represented as 'g'?

9.8 m/sec Signup and view all the answers

How does the mass of the moon affect its gravity compared to Earth?

It has 1/6 the mass of Earth, resulting in lower gravity Signup and view all the answers

What is the total energy of a falling mass at its highest elevation?

Maximum potential energy and zero kinetic energy Signup and view all the answers

What does the term 'mass' refer to in physics?

The amount of matter contained in a body Signup and view all the answers

What is the SI unit of energy?

Joule Signup and view all the answers

When an object falls, what happens to its potential energy?

It is converted to kinetic energy Signup and view all the answers

Which principle explains the attractive force between objects in the universe?

Gravitation Signup and view all the answers

On the moon, what is the acceleration due to gravity?

1.63 m/sec² Signup and view all the answers

What concept describes the amount of motion an object has in relation to its mass and velocity?

Momentum Signup and view all the answers

What effect does rolling one surface over another have in comparison to sliding one surface?

It creates less friction. Signup and view all the answers

What is the primary source of energy for all life on Earth?

The sun Signup and view all the answers

What typically happens to heat produced by friction?

It is often a loss of energy. Signup and view all the answers

Efficiency in a simple machine is calculated as what?

Work output divided by work input Signup and view all the answers

What is the result when 100 joules of work is put into a gear train that outputs 90 joules?

90% efficiency Signup and view all the answers

Which of the following statements about energy is correct?

Energy can neither be created nor destroyed. Signup and view all the answers

Which method is NOT commonly associated with generating heat?

Magnetism Signup and view all the answers

What does the efficiency of a more complex machine measure?

The ratio of work output to energy input Signup and view all the answers

What does gyroscopic rigidity refer to?

The property of a rotating mass to resist changes to its plane of rotation. Signup and view all the answers

What is the result of applying an external force to a rotating mass?

It causes the plane of rotation to change direction, known as precession. Signup and view all the answers

If an aircraft pitches nose down, what direction does the precession occur?

Yaw left. Signup and view all the answers

Which of the following best describes gyroscopic inertia?

The tendency of a rotating gyroscope to maintain its plane of rotation. Signup and view all the answers

What happens to the plane of rotation when a force is applied to a gyroscope?

It deflects 90° in the direction of rotation. Signup and view all the answers

Which characteristic allows a gyroscope to display an aircraft's attitude effectively?

Gyroscopic inertia. Signup and view all the answers

In dynamics, what does precession specifically refer to?

The effect of an external force causing a change in plane of rotation. Signup and view all the answers

Which of the following is NOT a characteristic of a gyroscope?

Linear acceleration Signup and view all the answers

Study Notes

Module: B-2 Physics, Topic 2.2.3 Dynamics

Introduction: This module covers fundamental physics concepts related to dynamics, including mass, force, inertia, work, power, energy (potential, kinetic, and total), resultant force, equilibrium, heat, efficiency, momentum, conservation of momentum, impulse, gyroscopic principles, friction, its nature and effects, and the coefficient of friction (rolling resistance).

Gravity

Definition: Gravity is the natural force of attraction between all objects in the universe.
Orbital Effects: Gravity keeps planets in orbit around the sun.
Weight: On Earth, gravity gives objects the property of weight.
Direction of Force: Gravity causes unsupported objects to fall toward the center of the Earth.
Acceleration Due to Gravity (g): The acceleration due to Earth's gravity is 9.8 m/s².
Weight Calculation: Weight (W) = mass (m) × acceleration due to gravity (g). This calculation is used to determine the force acting on a falling body.
Weight on the Moon: The acceleration due to gravity on the moon is significantly less than on Earth (approximately 1/6th). This results in a proportionally lower weight for the same mass.

Mass and Weight

Mass: The amount of matter in an object. It remains constant regardless of location.
Weight: The force of gravity acting on an object's mass. It varies depending on the gravitational field.
Relationship between Mass and Weight: Weight is calculated by multiplying mass by the acceleration due to gravity.
Example: A person with a mass of 100 kg on Earth will weigh 100 kg × 9.8 m/s² = 980 N (Newtons). Their weight on the moon will be significantly less due to the lower gravitational acceleration.

Inertia

Definition: Tendency of an object to resist any change in its state of motion or rest.
Newton's First Law: A body at rest stays at rest or continues its uniform motion in a straight line unless acted upon by an external net force.
Mass and Inertia: The greater the mass of an object, the greater its inertia.

Work

Definition: Done when a force acts on an object and moves it a distance.
Calculation: Work (W) = Force (F) × distance (d).
SI Unit: Joule (J)
Zero Work: No work is done if the object doesn't move.
Imperial Unit: Foot-pound (ft-lb)

Power

Definition: Rate at which work is done.
Formula: Power (P) = Work (W) / Time (t)
Unit: Watt (W) (joules per second)
Example Scenario: The power a person uses to climb stairs is different whether walking or running. Running at a faster rate requires more power. The same work is being done though.
Horsepower (hp): 550 foot-pounds of work in one second.

Energy

Definition: The capacity for doing work or producing change.
SI Unit: Joule (J).
Law of Conservation: Energy cannot be created or destroyed, only transformed from one form to another.
Types: Potential, Kinetic, and Total

Potential Energy

Definition: Energy stored in a body due to its position, condition, or chemical nature.
Examples in context: A weight held aloft has potential energy.

Kinetic Energy

Definition: Energy a body possesses due to its motion.
Example: A falling object gains kinetic energy as it moves.
Kinetic Energy Formula: Kinetic energy (KE) = 1/2 × mass (m) × velocity² (v²)

Total Energy

Definition: The sum of all potential energy (PE) and kinetic energy (KE) in a system. -Conservation of Energy: Total energy remains constant during transformation.

Friction

Definition: Resistance to motion between two surfaces in contact.
Types: Static, sliding, and rolling.
Coefficient of Friction: Indicates the friction between two different materials.
Steel-on-steel example: The coefficient of friction of steel on steel is 0.09.
Tyre/runway example: Rubber on dry/wet runway coefficient of friction is 0.7/0.5 respectively.
Teflon-on-Teflon example: The coefficient of friction of Teflon on Teflon is 0.04.
Rolling Resistance: Example: Tire on a road or ball bearings have very low coefficients of friction and are desirable to have low resistance.
Minimising Friction: Lubricating surfaces minimises friction.
Calculating Sliding Friction: F=μN with N being the reaction to the weight from the surface. The larger the coefficient of friction (μ), the greater the resistance.

Momentum

Definition: A measure of the tendency of a moving body to continue in motion along a straight line. (Linear Momentum).
Formula: Momentum (M) = mass (m) × velocity (v)
Conservation of Momentum: If two or more bodies collide and stick together, the total momentum remains the same before and after the collision.
Angular Momentum: Tendency of a spinning object to continue spinning.

Impulse

Definition: Change in momentum when a force is applied for a period of time.
Formula: Impulse (I) = Force (F) × Time (t)
Example: A spacecraft's thrust produces an impulse.

Gyroscopic Properties

Gyro-rigidity: The natural tendency of a rotating body to maintain its axis of rotation. This can be used to aid in aircraft attitude display.
Gyro-precession: A change in the plane of rotation of a rotating body caused by an external force. This allows gyroscopic systems to sense turns in aircraft.

Heat

Definition: A form of energy resulting from the motion of atoms or molecules.
Source: The sun.
Examples: Combustion of wood or electrical appliances.

Efficiency

Definition: A measure of how much of the input energy is used to do useful work.
Formula: Efficiency = (useful work output / total energy input).

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Description

Test your understanding of work, power, and friction in physics. This quiz covers fundamental concepts including the calculation of work, the impact of force and distance, and the various types of friction encountered in daily scenarios. Perfect for physics students looking to reinforce their knowledge!