What Is Work? | Physics in Motion

GPB Education
6 Feb 201908:26
EducationalLearning
32 Likes 10 Comments

TLDRThis educational video script explores the concept of work in physics, distinguishing it from everyday tasks. It explains that work occurs when a force causes displacement, and is calculated as force times distance, measured in joules. The script clarifies that work can be positive, negative, or zero, depending on the direction of force and movement. It also touches on the relationship between work, energy, and the conservation of energy, using examples from daily life and sports to illustrate these principles.

Takeaways
  • 🔧 Work in physics is defined as when a force causes an object to move or be displaced, requiring acceleration.
  • 📚 Work can be calculated using the formula: force (F) times displacement (d) equals work (W), measured in joules.
  • 📏 The direction of force and displacement is crucial; work is positive when they are in the same direction, negative when opposite, and zero when perpendicular.
  • 🎯 Scalars like work and energy do not have direction but can have positive or negative values depending on the context.
  • 🚫 No work is done when an object does not move or moves at a constant speed, regardless of the force applied.
  • 💪 Examples of work include lifting a box, a dancer being lifted, or a weightlifter picking up a weight.
  • 🤔 Work is not done by just sitting at a computer; it involves applying force, such as typing on the keys.
  • 🏈 The work done by friction or a defender in football is negative because it slows down the motion of an object, transferring energy out of the system.
  • 🧩 The Law of Conservation of Energy states that energy cannot be created or destroyed, only transferred or changed in form.
  • 🌐 A system can be anything from the human body to the entire galaxy, depending on what is being studied.
  • 🔄 Energy transfer through work can be positive (adding energy) or negative (removing energy), affecting the system's total energy.
Q & A

  • What is the specific meaning of 'work' in physics?

    -In physics, 'work' refers to the process where a force causes an object to move or be displaced. Work is done when an object accelerates, and it requires both a force and a displacement in the direction of the force.

  • What are the two essential components needed to calculate work in physics?

    -The two essential components needed to calculate work are the force (F) applied to an object and the displacement (d) of the object in the direction of the force.

  • What is the formula to calculate work in physics?

    -The formula to calculate work (W) in physics is the product of the force (F) and the displacement (d), which is expressed as W = F * d.

  • What unit is used to measure work in physics, and how is it derived?

    -The unit used to measure work in physics is the joule (J). It is a derived unit that combines newtons and meters, representing the work done when a force of one newton moves an object one meter.

  • How can work be positive, negative, or zero, and what determines this?

    -Work can be positive when the force and displacement are in the same direction, negative when they are in opposite directions, and zero when there is no displacement despite the presence of force.

  • What is the relationship between work and energy?

    -Work is a transfer of energy from one object to another. The ability to do work is a measure of the energy that can be transferred. The Law of Conservation of Energy states that energy cannot be created or destroyed, only transferred or changed in form.

  • What is a system in the context of energy and work?

    -A system is a defined area or collection of objects that are being studied in relation to energy and work. It can range from a simple object like a ball to complex entities like the human body or even the Earth.

  • How does the concept of a closed system relate to the study of energy and work?

    -A closed system is one that is isolated from the outside world, meaning no energy or matter can enter or leave. In the context of energy and work, it simplifies the study by assuming no external interactions.

  • What is the difference between positive and negative work in the context of lifting and dropping a box?

    -Positive work is done when lifting a box, as the force applied (upward) and the displacement (upward) are in the same direction. Negative work is done when dropping a box, as the force of gravity (downward) and the displacement (downward) are in the same direction, but the work done by the person lifting the box is in the opposite direction of the displacement.

  • How is work calculated for the football players pushing a sled in the given example?

    -The work done by the football players on the sled is calculated using the formula W = F * d, where F is the force applied (found using F = m * a), m is the mass of the sled, a is the acceleration, and d is the displacement. In this case, W = (300 kg * 0.25 m/s² * 15 m) = 1,125 joules.

  • Why is the work done by gravity and the normal force considered zero when pushing the sled?

    -The work done by gravity and the normal force is considered zero because these forces act perpendicular to the motion of the sled. Since work is only done when the force and displacement are in the same direction, perpendicular forces do not contribute to the work.

Outlines
00:00
🔧 Physics of Work: Definition and Calculation

This paragraph introduces the concept of work in physics, contrasting it with everyday notions of work. It explains that in physics, work is done when a force causes an object to move or be displaced, and it requires acceleration. The formula for work is presented as the product of force and displacement, resulting in a unit called a joule. The paragraph further explores the scalar nature of work, its positivity, negativity, and the concept of zero work. It also discusses the directional aspect of work, using examples such as lifting a box and the work done by gravity. The summary concludes with examples of work in various everyday activities, emphasizing that work in physics is specifically about the mechanical energy transfer.

05:02
🏈 Work and Energy in Physics: Calculations and Conservation

The second paragraph delves deeper into the physics of work, starting with a practical example of football players pushing a sled, and how to calculate the work done on it using the force equation. It explains the concept of a system in physics and distinguishes between closed and open systems. The paragraph then connects work with energy, describing energy as the ability to do work and emphasizing its scalar nature with positive or negative values. The Law of Conservation of Energy is alluded to, indicating that energy can neither be created nor destroyed, only transferred or transformed. The summary ends by reinforcing the idea that work is a transfer of energy and provides an example of the human body as a system, illustrating how energy enters and exits the system in different forms.

Mindmap
Keywords
💡Work
In the context of the video, 'work' is a physics term that describes the process where a force causes an object to move or be displaced. It is a scalar quantity and can be positive, negative, or zero, depending on the direction of the force relative to the displacement. The video emphasizes that work in physics differs from everyday usage, such as doing chores, studying, or writing. For example, when lifting a box, if the force and displacement are in the same direction, it is positive work.
💡Force
Force is a push or pull upon an object resulting from its interactions with another object. In the video, force is a necessary component for work to be done in physics. The amount of force applied to an object, such as when mowing the lawn or hitting a tennis ball, is crucial in calculating the work done on the object. The script uses the example of 15 newtons of force moving an object 4 meters to illustrate the calculation of work.
💡Displacement
Displacement refers to the change in position of an object. In physics, it is the term used to describe the distance an object moves in a specific direction, which is essential for calculating work. The video script explains that work is calculated as the product of force and displacement, and it uses the formula W = F * d to illustrate this concept.
💡Joule
The joule is the unit of measurement for work in the International System of Units (SI). It is a derived unit that combines newtons and meters, as seen in the script's example where 15 newtons of force applied over 4 meters results in 60 joules of work. The video emphasizes that a joule is a scalar quantity, indicating the amount of work done without a direction.
💡Positive Work
Positive work occurs when the force applied to an object and the object's displacement are in the same direction. The video script illustrates this with the example of lifting a box upward, where the force and displacement are aligned, resulting in positive work being done on the box.
💡Negative Work
Negative work is done when the force is applied in one direction while the object moves in the opposite direction. The video uses the example of gravity acting on a box when it is dropped; the gravitational force is downward, and the displacement is also downward, resulting in positive work by gravity, but negative work from the perspective of lifting the box against gravity.
💡Zero Work
Zero work is said to occur when there is no displacement in the direction of the applied force. In the video, an example given is holding a box without moving it; no work is done because there is no displacement, even though a force is applied.
💡Friction
Friction is a force that opposes the relative motion or tendency of such motion of two surfaces in contact. The video script explains that the work done by friction is negative because it slows down the motion of an object, transferring energy out of the object's movement, such as a football player being tackled and slowed down by a defender.
💡Energy
Energy is the capacity to do work. The video script discusses energy in the context of work, stating that work transfers energy from one object to another. It also introduces the concept of the Law of Conservation of Energy, which implies that energy cannot be created or destroyed, only transformed from one form to another.
💡System
A system, in the context of the video, is a defined area or collection of objects being studied. It could be as small as the human body or as large as the Earth or the entire galaxy. The script explains that energy can enter and leave a system, and the study of work and energy within a system is crucial for understanding physical phenomena.
💡Conservation of Energy
The Law of Conservation of Energy states that energy cannot be created or destroyed in an isolated system, only transformed from one form to another. The video script refers to this principle to explain how work is related to energy, emphasizing that the total energy in a closed system remains constant.
Highlights

Work in physics is defined as the process where a force causes an object to move or be displaced.

An object must accelerate for work to be done; no work is done if it moves at a constant speed or doesn't move.

The amount of work done is calculated by the formula: force times displacement equals work.

The unit of work is the joule, a derived unit combining newtons and meters.

Work can be positive, negative, or zero, depending on the direction of force and displacement.

Positive work occurs when force and displacement are in the same direction, such as lifting a box upwards.

Zero work is done when an object is held without moving, indicating no displacement.

Negative work is done when the direction of force is opposite to the direction of displacement, like lifting a box against gravity.

Work is not done when force and movement are perpendicular to each other, such as pushing a box sideways while lifting upwards.

The direction of work is determined by the direction of motion, like vertical work when lifting a box.

Friction does negative work by slowing down the forward motion of an object, similar to a defender slowing down a ball carrier.

The total work done on an object can be calculated using the formula: mass times acceleration times displacement.

In the example of football players pushing a sled, the work done is 1,125 joules over a 15-meter displacement.

Gravity and normal force do no work when they are perpendicular to the motion, as in the sled example.

Work transfers energy from one object to another, and energy is the ability to do work.

A system in physics can be any collection of objects being studied, such as the human body or the entire galaxy.

The Law of Conservation of Energy states that energy cannot be created or destroyed, only transferred or changed in form.

Energy and work are scalar quantities, which means they have magnitude but no specific direction.

Transcripts

Browse More Related Video

Positive & negative work | Work & Energy | Physics | Khan Academy

Work and Energy : Definition of Work in Physics

Work and Energy in Physics

Positive and negative work |⚡3d animation | Class 9, Physics |

Work and Kinetic Energy - Physics

High School Physics - Work

Rate This

5.0 / 5 (0 votes)

Thanks for rating:

Related Tags
PhysicsWorkEnergyConservationForceDisplacementJouleMechanicalChemical EnergyFrictionMotion