Work as the transfer of energy | Work and energy | Physics | Khan Academy

Summary

The script explains the concept of work done through the formula Fd cos(theta), highlighting its relation to energy transfer. It illustrates positive work with a skateboarder gaining kinetic energy and negative work with the skateboarder losing energy upon crashing. The script further clarifies the principle using gravitational potential energy, showing how lifting bricks results in positive work done. It concludes by emphasizing that work can be determined by the energy an object gains or loses, applicable to all forms of energy.

Takeaways

• 🔍 The formula for work done is Fd*cosine(theta), which represents the energy transferred to an object.
• 🚀 Positive work done (+200 joules) means the force gives energy to an object.
• 🛑 Negative work done (-200 joules) signifies the force takes energy away from an object.
• 🛴 An example is a 50-kilogram skateboarder who gains 2,500 joules of kinetic energy when moved by a force.
• 🏋️‍♂️ The skateboarder's kinetic energy is the measure of the positive work done by the force.
• 💥 When the skateboarder crashes into a stack of bricks, the bricks do negative work by removing energy.
• 🧱 The work done by the bricks is calculated by the energy they took away from the skateboarder.
• 📈 Lifting bricks upwards transfers energy to them in the form of gravitational potential energy.
• 📐 Gravitational potential energy is calculated using the formula mgh, where m is mass, g is acceleration due to gravity, and h is height.
• 🌐 The concept of work done applies to all types of energy, not just kinetic and potential energy.

Q & A

What is the formula used to calculate the amount of work done?

The formula used to calculate the amount of work done is Fd cosine theta.

How does the amount of work done relate to energy transfer?

The amount of work done represents the amount of energy transferred to an object.

What does a positive value of work done indicate?

A positive value of work done indicates that the force gave energy to the object.

How much kinetic energy did the skateboarder gain when moving at 10 meters per second?

The skateboarder gained 2,500 joules of kinetic energy.

What is the relationship between force and work when the skateboarder crashes into a stack of bricks?

The stack of bricks does negative work on the skateboarder because it takes away energy from the skateboarder.

How much work is done by the bricks on the skateboarder when they come to a stop?

The work done by the bricks on the skateboarder is negative 2,500 joules.

What type of energy is gained by the bricks when they are lifted upwards?

The bricks gain gravitational potential energy when they are lifted upwards.

What is the formula to calculate gravitational potential energy?

The formula to calculate gravitational potential energy is mgh.

How much gravitational potential energy did the 500-kilogram bricks gain when lifted four meters?

The bricks gained 19,600 joules of gravitational potential energy.

What does it mean when a force gives energy to an object?

When a force gives energy to an object, it is doing positive work on that object.

Can the concept of work done be applied to all types of energy?

Yes, the concept of work done can be applied to all types of energy, not just gravitational potential energy and kinetic energy.