3D3 Work and Power Flashcards
Learn the fundamental concepts of work, energy, and power, and how they are measured and calculated.
How is the term “work” defined in physics?
The product of a force acting on an object and the displacement of that object in the direction of the force.
Describe what happens when a person picks up a book in terms of work?
The muscles in the person’s arm apply force to the book and work against gravity, performing work.
What unit is used to measure work or energy in physics?
joules (J)
How much energy is one joule equivalent to in terms of force and distance?
One joule is equivalent to the work done by a force of one newton moving an object one meter in the direction of the force.
How can energy (work) be calculated?
- Energy (J) = Force (N) × Distance (m)
or - Work (W) = Force (F) × Displacement (d)
These formulae assumes that the force is constant and applied in the direction of the displacement. If the force varies, the work done is the integral of the force over the path of displacement.
Why is understanding work important for understanding simple machines?
Because it explains how energy is transferred and how forces are applied to move objects.
How is work in physics different from work in everyday life?
- In physics, work is a quantitative measure of energy transfer when an object is displaced by an external force.
- In everyday life, work refers to any activity involving physical or mental effort.
Can work be positive, negative, or zero? Explain.
- Yes, work can be positive when force and displacement are in the same direction.
- Negative when they are in opposite directions.
- Zero when there is no displacement or the force and displacement are perpendicular.
Give an example of positive work.
Pushing an object on a smooth horizontal surface.
e.g. riding a bicycle
What is an example of negative work?
Throwing an object in the air.
Where gravity acts in the opposite direction to the displacement.
What happens to work when the force and displacement are perpendicular?
The work done is zero.
What is the formula for work that includes the angle between force and displacement?
Work (W) = Force (F) × Displacement (d) × Cosine (θ)
How does the angle between the vectors affect the calculation of work?
- If the angle is between 0 and 90 degrees, work is positive.
- If between 90 and 180 degrees, work is negative.
- If 90 degrees, work is zero.
Why is work considered a scalar quantity?
Because it has magnitude but no direction.
How is work related to energy?
Work is a measure of energy transfer.
When work is done on an object, energy is transferred to or from that object. For example, lifting an object increases its gravitational potential energy.
What is the role of cosine in the work formula involving angles?
Cosine of the angle between force and displacement vectors determines the magnitude and sign of the work.
Explain why work can be both a scalar quantity and depend on direction.
Work is scalar because it represents the magnitude of energy transfer without direction; however, the sign of work depends on the direction of force and displacement vectors.
A scalar is a quantity that is fully described by a single value or magnitude. It does not have direction, unlike a vector which has both magnitude and direction.
How does friction affect the work done on an object?
It does negative work on an object because it opposes the direction of displacement.
Why is it useful to draw a free-body diagram when calculating work?
It helps identify the direction and magnitude of all forces acting on an object, which is essential for accurately calculating work.
How does the direction of force affect the calculation of work?
It determines whether the work is positive, negative, or zero.
What is the significance of James Watt in the context of power?
The unit of power, the watt (W), is named after him in recognition of his contributions to the development of the steam engine and the study of power.
