AP PHYSICS unit 2

What is the unit for mass?

Kilograms(Kg)

What is inertia?

An object’s resistance to changes in its velocity.

What is velocity?

The rate of change of position, including direction.

What is the units for velocity?

m/s

What is speed?

How fast an object moves, without specifying direction

What is acceleration?

The rate of change of velocity.

What is the units for acceleration?

m/s².

What is the average-acceleration equation?

a = (v_final − v_initial) / Δt

Can an object accelerate at constant speed?

Yes. Changing direction changes velocity, even at constant speed

What is a force?

A push or pull caused by an interaction. Unit: newton (N)

What is net force?

The vector sum of all forces acting on an object

What does a negative force mean?

The force points opposite the chosen positive direction

What is one newton?

The net force that accelerates 1 kg at 1 m/s²

What is the difference between force and net force?

Force is an individual interaction; net force combines all forces

What is a system in physics?

The object or collection of objects selected for analysis

What is the surroundings of a system?

Everything outside the chosen system.

What is an external force?

A force exerted on the system by something outside it

What is an internal force?

A force arising from interactions between parts of the system.

What is the center of mass (COM)?

The mass-weighted average position of a system.

What is the center-of-mass equation along x?

x_COM = Σ(mᵢxᵢ) / Σmᵢ

What is the center-of-mass equation along y?

y_COM = Σ(mᵢyᵢ) / Σmᵢ

How do you find the COM of two objects?

Multiply each mass by its position, add, then divide by total mass

Where is the COM of two equal masses?

Halfway between their positions

Where is the COM relative to a heavier object?

It lies closer to the heavier object

Must the COM lie inside an object?

No. A uniform ring’s COM is at its empty center

What is the continuous COM equation?

x_COM = (1/M) ∫ x dm

What is linear mass density?

Mass per unit length, represented by λ

How is a tiny mass element written for a rod?

dm = λ(x) dx

Where is the COM of a uniform rod?

At its midpoint, L/2, measured from either end.

What determines a system’s COM acceleration?

The net external force: F_net,external = M a_COM.

Do internal forces change a system’s COM motion independently?

No. The COM acceleration depends on the net external force.

How do you find the total mass of a system?

Add the masses of all objects in the system.

What is a common COM calculation mistake?

Averaging positions without weighting them by mass.

What is another common COM mistake?

Using individual mass instead of total system mass for a__COM.

What is a free-body diagram (FBD)?

A diagram showing all external forces acting on one chosen object.

What is the first step in drawing an FBD?

Isolate the object you are analyzing.

What should an FBD include?

The object, force arrows, labels, and force directions.

What is the most important FBD rule?

Draw only forces acting on the chosen object

What is gravitational force near Earth’s surface?

F_g = mg, directed downward.

What is the normal force?

A contact force perpendicular to the contacting surface.

When does the normal force equal mg?

On a horizontal surface with no other vertical forces and zero vertical acceleration

What is tension?

A pulling force transmitted along a taut rope, string, or cable.

What direction does tension act?

Along the rope, pulling away from the attached object.

What is an applied force?

A push or pull exerted by a person or another object.

What direction does friction act?

Along the contact surface, opposing relative sliding or its tendency

What direction does a spring’s restoring force act?

Toward the spring’s equilibrium position.

What is air resistance?

A resistive force opposing motion relative to air

What are the horizontal and vertical force equations?

ΣF_x = ma_x; ΣF_y = ma_y

How do you choose axes for an inclined plane?

Usually parallel and perpendicular to the ramp