8.3 Work and Energy

What is energy in physics?

Energy is a fundamental property of nature.

Why is energy important in physics?

It helps us understand how the universe works and how systems behave.

How is energy related to work?

Energy is related to the amount of work that can be done.

What is the simple definition of energy?

Energy is the ability to do work.

Can energy exist in different forms?

Yes, energy can be found in many forms.

What happens to energy in physical systems?

Energy is always transformed from one form to another.

What are the SI units of energy?

Joules (J)

What does it mean when we say energy is transformed?

It means energy changes form but is not lost.

What are examples of forms of energy?

Thermal, light, chemical, electrical

What happens when work is done on a system?

Energy is transferred.

What must happen for work to be done?

A force must be applied and there must be displacement in the direction of that force.

What are the two requirements for work to occur?

Force is exerted and displacement occurs in the same direction.

Is work done if you push something and it does not move?

No, because there is no displacement.

Is work done if an object moves but no force is applied?

No, because there is no force.

Is work done if force and displacement are in different directions?

No, displacement must be in the direction of the force.

What is the equation for work?

W = Fd cos(theta)

What does W represent in the work equation?

Work (Joules)

What does F represent in the work equation?

Force (Newtons)

What does d represent in the work equation?

Displacement (meters)

What does theta represent in the work equation?

The angle between force and displacement

When is work maximized?

When force and displacement are in the same direction (theta = 0 degrees)

When is work equal to zero due to angle?

When theta = 90 degrees

What part of a force does work when applied at an angle?

The component of the force in the direction of displacement (F cos(theta))

What is the work equation when force and displacement are parallel?

W = Fd

Why does W = Fd when theta = 0 degrees?

Because cos(0) = 1 so all the force contributes to work.

Is any force wasted when force and displacement are parallel?

No, all of the force contributes to motion.

What is the work done when holding an object still?

0 Joules

Why is work zero when holding a briefcase motionless?

Because displacement is zero.

Can work be done if force is applied but there is no movement?

No, displacement must occur.

Why do you get tired holding a briefcase if no work is done on it?

Because your muscles are doing internal work and using energy.

Where is work being done when holding an object still?

Inside your muscles, not on the object.

What is the work done when force is perpendicular to displacement?

0 Joules

What angle between force and displacement results in zero work?

90 degrees

A person carries a briefcase horizontally at constant speed. Is work done on the briefcase?

No, force is vertical and motion is horizontal.

How do you calculate work when force is at an angle?

W = Fd cos(theta)

Why do we use cos(theta) in the work equation?

To get the component of force in the direction of motion.

In angled force problems, which part of the force does work?

The component parallel to displacement.

What is the work done when a 10 N force moves an object 5 m at 20 degrees?

Approximately 47 J

Which force does the most work: 10 N vertical, 8 N at 60 degrees, or 6 N horizontal?

The 6 N force.

Does the largest force always do the most work?

No, only the component in the direction of motion matters.

Why does a 10 N vertical force do zero work?

It is perpendicular to displacement (theta = 90 degrees).

What determines how much work a force does?

The component of the force parallel to displacement.