Winter term Devaney Physics

Newton’s first law

An object at rest stays at rest, and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an external force.

Newton’s second law

Acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. It can be mathematically expressed as F = ma, where F is the net force, m is the mass of the object, and a is the acceleration.

Newton’s third law

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

Inertia

The tendency of an object to resist changes in its state of motion. It is directly proportional to an object's mass, meaning the more massive an object is, the greater its inertia.

(1st law)

Magnitude

Size of something

Direction

self explanatory

Scalar quantities

Values with only magnitude, no direction

Ex. mass, speed, distance, energy, time, temperature

Vector quantities

Values with magnitude and direction

Ex. velocity, force, acceleration, displacement

Mechanical equilibrium

All net forces equal zero

Static equilibrium

Object is in mechanical equilibrium so that it does not move

Dynamic equilibrium

Object that is in mechanical equilibrium, but at a constant velocity so that all forces equal zero.

Already in motion but since constant all forces equal zero

Normal force

Force perpendicular to the surface an object is o

Average speed

Average speed is explanatory, but the important part is it has no direction. So total distance travelled is what needs to be paid attention to.

Equation form: average speed = total distance travelled / time

Average velocity

Like average speed but it is important to know that velocity has direction. So taking that into consideration, total displacement is over time. So if I walk 2 miles left in an hour, but 3 miles right in another hour, the average velocity is 0.5 miles per hour right.

Equation form: average velocity = total displacement / time

Acceleration

The rate of which speed increases.

Equation: a = velocity final - velocity initial / time

How to calculate net force

Add all the forces acting on an object to get net force (keep in mind possible negative values from direction)

Friction Force

The force that resists motion when the surface of one object comes in contact with the surface of another.

Mew

Static friction

The friction force of an object at rest

Larger than kinetic

Kinetic friction

The friction force of an object at rest

Smaller than static or else things wouldn’t be able to move

The transfer of static friction into kinetic friction

As an object slides more, gravity can’t lock in microscopic nooks so that kinetic friction is always less

Weight

The force of gravity x mass

Weight on an incline

Same as the weight on a horizontal surface and freefall

Weight in freefall

Same as the weight on a horizontal surface and freefall

Normal force on a horizontal surface

Equal to weight of object/force acting upon it

Normal force on a incline

Only equal to the force pushing down on it and isn’t necessarily equal to the object’s weight

Normal force in freefall

0 since it is in motion and gravity is parallel to surface

Net forces on an incline or with diagonal forces

Use Pythagorean theorem to find the net force by finding the hypotenuse of vector quantities.

With an incline use the Normal and Parallel forces as the ‘legs’ or a and b to find the vector for gravity

Or do the opposite by c² - a² = b²

Momentum

It is a vector quantity that describes the motion of an object and is conserved in a closed system.

Equation: momentum=mass x velocity

Impulse

J= force x time

Relationship of momentum and impulse

change of momentum = impulse

mvf-mvi=ft

Conservation of momentum

In the absence of an external force, the momentum of a system remains unchanged.

Elastic collision

collision of stuff that bounces off each other

mvai+mvbi=mvaf+mvbf

Inelastic collision

collision of stuff that stick together

mvai+mvbi= (ma+mb) vf

Work

work it takes to do stuff

work=force x distance

Potential energy

The value for amount of stored energy, which means PE equals KE

gravitational pe: pe=mass x gravity x height

Kinetic energy

Energy of motion

ke=1/2mv²

Work energy theorem

the net work done by the forces on an object equals the change in its kinetic energy

so Work=KEf-KEi

or Work=PE

the work you do to move an object a distance is equal to its change of energy

Conservation of energy

no energy dissipates, it changes forms

Thermal energy

what most energy transfers into because of compression of atoms

Clearest way to see energy

when its being transformed