Work and Energy : Definition of Work in Physics
TLDRIn this educational video, the presenter clarifies the physics concept of work, distinguishing it from everyday usage. The video begins with the physics definition of work, which occurs when a force causes a displacement. The formula for calculating work is introduced as force multiplied by displacement in the direction of the force. To illustrate, an experiment is conducted with a book, demonstrating the work done when lifting it against gravity. The video then explores the scenario where force and displacement are not aligned, introducing the formula W = F * s * cos(θ), where θ is the angle between force and displacement. Three cases are discussed: when force and displacement are in the same direction (θ = 0°), when a person carries a bag (θ = 90°, resulting in no work done by the lifting force), and when lifting a book against gravity (θ = 180°, yielding negative work). The video concludes with a reminder of the difference between physics work and everyday work, and encourages viewers to engage with the content by liking, commenting, and subscribing.
Takeaways
- 📚 The physics definition of work is different from everyday use; it involves a force and displacement.
- 🧮 The formula to calculate work done is force multiplied by displacement in the direction of the force (W = F * s).
- 📐 When force and displacement are not in the same direction, work is calculated using W = F * s * cos(θ), where θ is the angle between force and displacement.
- 📈 Work done can be positive (force and displacement in the same direction) or negative (force and displacement in opposite directions).
- 📌 When the angle between force and displacement is 0 degrees, the work done is simply force times displacement.
- 🚫 When the angle is 90 degrees, no work is done in the direction of the force (e.g., carrying a bag while walking).
- 🔽 The work done by the force of gravity is negative when the force and displacement are in opposite directions, such as lifting a book upwards against gravity.
- 📝 It's important to consider the force involved and the direction of displacement when calculating work.
- 🔄 The concept of work is closely related to the change in energy, specifically kinetic energy.
- 📚 For a deeper understanding of work in relation to energy, one should study the topic of energy.
- 💡 The video provides three exam-oriented questions to test the understanding of the concept of work.
- 📢 The presenter encourages viewers to like, comment, share, and subscribe for more informative content.
Q & A
What is the physics definition of work?
-In physics, work is done when there is a force applied to an object and the object experiences a displacement in the direction of the force.
What is the formula to calculate work done?
-The formula to calculate work done is force multiplied by displacement in the direction of the force, which can be written as W = F * d, where W is work, F is force, and d is displacement.
How do you calculate work done when the force and displacement are not in the same direction?
-When the force and displacement are not in the same direction, work done is calculated using the formula W = F * d * cos(theta), where theta is the angle between the force and the displacement.
What is the SI unit for work done?
-The SI unit for work done is the joule (J), which is equivalent to a newton meter (Nm).
What happens if there is no displacement of an object, even though a force is applied?
-If there is no displacement, even though a force is applied, no work is done on the object. Work requires both force and displacement.
What is the relationship between work done and the angle between force and displacement?
-The relationship is that the work done is maximum when the force and displacement are in the same direction (0 degrees) and can be zero or negative depending on the angle. For example, if the angle is 90 degrees, the work done is zero, and if the force and displacement are in opposite directions (180 degrees), the work done is negative.
Why does the work done by a person carrying a bag while walking turn out to be zero?
-The work done by the person carrying a bag while walking is zero because the force exerted by the person (upward to hold the bag) is perpendicular to the displacement (along the path of walking), and the cosine of 90 degrees is zero.
What is the significance of negative work?
-Negative work signifies that the force is acting in the opposite direction to the displacement. This often occurs when work is done against a force, such as lifting an object against gravity, where gravity does negative work.
Why is it important to consider the force involved and the displacement when calculating work done?
-It is important because the calculation of work is dependent on both the magnitude and direction of the force and the displacement. Failing to consider these accurately can lead to incorrect work calculations.
What is the second formula mentioned for calculating work done?
-The second formula mentioned for calculating work done is related to the change in energy, specifically the change in kinetic energy.
What is the implication of the force of gravity doing negative work when lifting a book?
-The implication is that as you lift the book against the force of gravity, gravity is doing negative work because the direction of the gravitational force is opposite to the direction of the displacement of the book.
How can you ensure that you understand the concept of work after watching the video?
-You can ensure understanding by pausing the video to take notes, especially after the concept board is presented, and by attempting to solve the top three exam-oriented questions provided at the end of the video.
Outlines
📚 Physics Definition of Work
The first paragraph introduces the topic of the video, which is the physics definition of work. The presenter explains that work in physics is different from everyday use of the term and is done when there is a force and a displacement in the direction of the force. The formula for calculating work done is force multiplied by displacement. The presenter then guides the audience to perform a simple experiment with a book to illustrate the concept of work. The example given involves lifting a book with a force of ten Newtons over a displacement of forty centimeters, which is converted to 0.4 meters, resulting in four joules of work done. The video also explores the scenario where force and displacement are not in the same direction, introducing the concept of the angle between the two and how to calculate work done in such cases.
🔍 Calculating Work Done with Different Angles
The second paragraph delves into the calculation of work done when the force and displacement are not aligned. The presenter explains that the work done can be calculated using the formula W = F * s * cos(theta), where theta is the angle between the force and the displacement. Three cases are discussed: when force and displacement are in the same direction (theta = 0 degrees), when a person carries a bag and the force is vertical while displacement is horizontal (theta = 90 degrees), and when lifting a book against gravity (theta = 180 degrees). The presenter emphasizes the importance of considering the force involved and the displacement when calculating work done and notes that work can be positive or negative depending on the direction of the force relative to the displacement.
📝 Exam-Oriented Questions and Further Learning
The final paragraph of the script provides a transition to the application of the concept of work through exam-oriented questions. The presenter encourages the audience to pause the video and attempt to solve three provided questions, promising a solutions video with a link in the video description. The presenter also briefly touches on the concept of work done being related to the change in energy, specifically kinetic energy, and invites viewers to watch another video on energy for more information. The video concludes with a call to action for viewers to like, comment, share, and subscribe to the channel.
Mindmap
Keywords
💡Work (Physics)
💡Force
💡Displacement
💡Formula
💡SI Unit
💡Cosine (cos)
💡Right Triangle
💡Kinetic Energy
💡Friction
💡Negative Work
💡Exam-oriented Questions
Highlights
The physics definition of work is different from everyday use, involving force and displacement.
The formula to calculate work done is force multiplied by displacement in the direction of the force.
An experiment is conducted using a book to illustrate the concept of work with and without displacement.
Work is only done when there is both a force and a displacement.
An example calculation is provided using 10 Newtons of force and 40 centimeters of displacement.
Work done is measured in joules, which is a newton meter.
When force and displacement are not in the same direction, work is calculated using the formula W = F * s * cos(theta), where theta is the angle between force and displacement.
Three cases are explored to apply the formula for work done: force and displacement in the same direction, force upward and displacement horizontal, and force of gravity acting in the opposite direction of displacement.
Work done can be positive or negative depending on the direction of force relative to displacement.
The video includes a concept board summarizing the formulas and cases for calculating work done.
Exam tips are provided to consider the force involved and the displacement when calculating work done.
The video concludes with a reminder that physics work differs from everyday language use and encourages further learning on the topic of energy.
The presenter uses a toy and a book to demonstrate the principles of work and force.
An interactive approach is taken, asking viewers to pause the video and participate in the experiment.
The importance of the direction of force relative to displacement is emphasized for calculating work done.
The concept of work is clarified with examples that include zero and 180-degree angles between force and displacement.
The video ends with an invitation to engage with the content by liking, commenting, and subscribing.
Additional resources are offered for further understanding, including a link to a solutions video and another on energy.
Transcripts
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