physics unit 5 & 6

Mass

Measure of an object's inertia.

Weight

Force of gravity on an object.

Weight Equation

Calculated with the equation w=mg.

Force

An action capable of causing acceleration (push or pull).

Unit of Force

Measured using the unit newton (N).

Net Force

The vector sum of all forces acting on an object.

Equilibrium

Objects with Fnet=0 are in equilibrium.

Static Equilibrium

Objects at rest.

Dynamic Equilibrium

Objects with constant velocity.

Inertia

Objects at rest will remain at rest unless acted on by a net force.

Gravity

All matter in the universe is attracted to all other matter.

Newton's 1st Law

Objects at rest will stay at rest unless acted on by a net force.

Newton's 2nd Law

ΣF=ma relates an object's acceleration, mass, and net force.

Newton's 3rd Law

Forces occur when two objects interact and come in pairs.

Action-Reaction Pairs

Force pairs are equal in magnitude and have opposite directions.

Four Fundamental Forces

Gravity, Electro-magnetic force, Strong nuclear force, Weak nuclear force.

Contact Forces

Exist between touching objects.

Field Forces

Exist without contact, e.g., gravity.

Normal Force

Force from a surface that acts perpendicular to the surface.

Applied Force

Generic term for a force between objects.

Thrust

Force from a jet engine, rocket engine, or propeller.

Tension

Force in (or from) a rope or chain.

Friction

Force that opposes sliding or prevents motion.

Free Body Diagrams

Show all forces acting on a single object.

What is a free-body diagram used for?

To identify all of the forces acting on an object.

What is the net force on an object represented by?

ΣF or Fnet, which is the vector sum of all forces acting on it.

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

The object has zero acceleration.

What does Newton's second law (ΣF=ma) help solve?

1D motion problems.

What effect does a force acting perpendicular to an object's velocity have?

It changes the object's direction but not its speed.

What is centripetal acceleration?

Acceleration that acts in the direction of the center of a circle.

What causes all circular motion?

A net force that is centripetal.

What is an example of circular motion?

Circular orbit.

What is the centripetal force that causes an object to orbit?

Gravity.

Why are objects in orbit considered weightless?

Because they are in freefall.

How is the force of gravity between two objects determined?

Using Newton's law of universal gravitation.

What is the equation for Newton's law of universal gravitation?

Fg = G * (m1 * m2) / d^2.

What do m1 and m2 represent in the gravitational equation?

The masses of the two objects.

What does 'd' represent in the gravitational equation?

The distance between the two objects.

What is the value of the gravitational constant (G)?

6.67×10^-11 N·m²/kg².

What is the acceleration due to gravity (g) near the Earth's surface?

9.8 m/s².

What is drag in physics?

The force of air resistance acting opposite to the direction of motion.

What does 'tangential' mean in the context of circular motion?

Pointing in a direction tangent to a circular path.

What is true about net force and acceleration in uniform circular motion?

They are centripetal, while velocity is tangential.

Can any force be centripetal?

Yes, any force can be centripetal in the right situation.

How can the value of g be calculated using Newton's law of universal gravitation?

By using the mass and radius of the Earth.

Gravity

attracts all matter in the universe to all other matter

Electro-magnetic force:

• the force of electric charges and magnets

Strong Nuclear Force

• holds the protons and neutrons together in the nucleus of atoms

Weak Nuclear Force

• causes beta decay (a type of radioactive decay)