Unit 2 Dynamics

What is a force?

A push or pull on an object; it's a vector quantity measured in newtons (N).

What are the four fundamental forces in nature?

Gravitational, electromagnetic, strong nuclear, weak nuclear.

What is the net force?

The vector sum of all forces acting on an object.

What is Newton’s First Law of Motion?

An object remains at rest or moves at constant velocity unless acted upon by a net external force.

What is inertia?

The tendency of an object to resist a change in motion; proportional to mass.

What happens when the net force on an object is zero?

The object remains at rest or continues to move at constant velocity.

What is Newton’s Second Law of Motion?

the acceleration of an object is directly related to the net force and inversely related to its mass

How does acceleration relate to mass and force?

Acceleration is directly proportional to net force and inversely proportional to mass.

If the net force is doubled on an object, what happens to acceleration?

It also doubles (assuming mass is constant).

What is Newton’s Third Law of Motion?

For every action force, there is an equal and opposite reaction force.

Do action-reaction forces act on the same object?

No, they act on different objects.

Give an example of Newton’s Third Law.

A swimmer pushes water backward; the water pushes the swimmer forward.

What are internal vs. external forces?

Internal forces act between objects in a system; external forces come from outside the system.

What is the weakest of the four fundamental forces of nature?

Gravity

Which object has the least inertia: a gas molecule, textbook, or Earth?

A gas molecule (less mass = less inertia)

Which of Newton’s Laws explains the jerking you feel when a vehicle stops suddenly?

Newton’s First Law (inertia)

Which of Newton’s Laws explains rocket propulsion in space?

Newton’s Third Law (action-reaction)

What happens to acceleration if the unbalanced force is doubled?

Acceleration doubles (Newton’s Second Law)

What happens to speed if the unbalanced force is doubled?

It cannot be determined without knowing time or acceleration.

If a 10 N downward force is added to a 20 N book on a table, what is the new normal force?

30 N (normal force balances total downward force)

What is the direction of friction?

Opposite to the motion or attempted motion.

What is the direction of the normal force?

Perpendicular and away from the surface.

What is terminal speed?

The speed at which air resistance equals gravity, resulting in no further acceleration.

Difference between mass and weight?

Mass is constant; weight is the gravitational force acting on that mass.

Define tension.

A pulling force transmitted through a rope, string, or cable.

What is an applied force?

A force that results when one object directly pushes or pulls another.

What is static friction?

The friction that prevents motion. It must be overcome to start moving an object.

What is kinetic friction?

The friction that acts against an object that is already moving.

What are action-at-a-distance forces?

Forces that act without physical contact, like gravity, electric, or magnetic forces.

What is apparent weight?

The normal force you feel, which can differ from your actual weight depending on acceleration (e.g., in an elevator).

When do you feel heavier than your actual weight?

When you're accelerating upward — your apparent weight (normal force) increases.

When do you feel lighter than your actual weight?

When you're accelerating downward — your apparent weight (normal force) decreases.