Forces Unit Flashcards

Comprehensive vocabulary flashcards covering terms, definitions, laws, units, and formulas from the Forces Unit notes.

Force

A push or pull on an object. It causes acceleration. Unit: newtons ($\text{N}$).

Mass

The amount of matter in an object. Unit: $\text{kg}$. Stays the same everywhere, even on the Moon.

Weight ($F_g$)

The force of gravity on an object. Weight = mass $\times$ $g$. Unit: $\text{N}$. Changes from planet to planet.

$g$ (acceleration of gravity)

$9.81\,\text{m/s}^2$ on Earth.

Inertia

An object's tendency to resist a change in its motion. Depends ONLY on mass: more mass = more inertia.

Net Force

The total of all forces on an object after adding them up and canceling opposites.

Equilibrium

Net force = $0$. The object is at rest OR moving at constant velocity.

Acceleration

A change in velocity: speeding up, slowing down, or changing direction. Unit: $\text{m/s}^2$.

Normal Force ($F_n$)

A surface pushing back on an object, at a right angle to the surface. On a flat floor, it equals the object's weight.

Friction ($F_f$)

A force that resists motion between surfaces that are touching.

Tension ($F_t$)

The pulling force carried by a rope, cable, or string.

Applied Force

A push or pull from a person or thing.

Air Resistance

Friction from air that pushes against a moving object.

Contact Force

A force that needs touching. Examples: friction, tension, normal, push, pull.

Field Force

A force that acts without touching. Examples: gravity, magnetism, electrical.

Newton's 1st Law (Law of Inertia)

An object stays at rest, or keeps moving at constant velocity, unless a net force acts on it. Ex: you lurch forward when a car brakes.

Newton's 2nd Law

$F = ma$. More force = more acceleration. More mass = less acceleration. Ex: a train needs more force to speed up than a car.

Newton's 3rd Law

Every action has an equal and opposite reaction. Ex: a rocket pushes gas down; the gas pushes the rocket up.

$$F = ma$$

Net force = mass $\times$ acceleration.

$$F_g = mg$$

Weight = mass $\times 9.81$.

$$a = \frac{F}{m}$$

Use this to find acceleration.

Net Force in 2D

Add all $x$ forces, add all $y$ forces, then: $\sqrt{x^2 + y^2}$.

Newton ($\text{N}$)

The unit for ANY force: weight, friction, normal, tension, net force.

$$\text{kg}$$

The unit for mass.

$$\text{m/s}^2$$

The unit for acceleration (including $g$).