physics unit 1

How is motion described

moving relative to something else

ex. the treadmill belt is moving and you are stationary

What is speed

distance covered per amount of travel time (distance/time)

What is instantaneous speed

speed at any instant (like a snapshot)

ex, speedometer that police use to see your mph

What is velocity

instantaneous speed and direction

How is velocity represented?

a vector quantity: magnitude (speed) is represented by length of vector and direction is represented by where vector points

What is acceleration and what can it involve?

• rate at which velocity changes over time (change in velocity/time interval)

• it can involve either a change in speed, direction or both

What does a steeper incline lead to and why?

greater acceleration because a greater portion of gravity points along the ramp so more of gravity is used to pull downhill

What does a vertical incline lead to and why?

max acceleration (falling object) because gravity is not split, so all of it is downhill

What happens when air resistance is negligible

all objects fall with the same acceleration because there is no air to push back differently on objects depending on size, weight, etc.

What is free falling

falling with gravity and no air resistance; falling in space/vacuum

What is acceleration on Earth

9.8 m/s²

What is velocity starting from rest

acceleration x time

What is Newton’s first law of motion

an object at rest tends to stay at rest unless acted upon by an outside force (inertia)

What is net force

sum of all forces acting on an object

What does the net force depend on

magnitude (strength) and direction of forces

Explain what is happening in this photo

• different angles —> different rope tensions will occur in each side

• Girl is hanging in equilibrium: tensions add to equal and opposite her weight

• tension in the right hand is greater than tension on the left side

What forces are acting on the girl?

gravity, tension (left), tension (right)

What’s happening in this photo

• two forces acting on the bag: string tension acts upward and gravity acts downward

• both force are equal in magnitude and opposite in direction so when added, they cancel to zero and the bag of flour remains at rest

What is support force?

upward force on an object opposite to gravity; balances an object's weight and keeps it from falling or moving through the surface

example: book on a table

• gravity pulls book downward

• atoms in the table are compressed

• pushes upwards against a compressive force

• provides a support force

What is equilibrium

a state of no change with no net force acting

What is static equilibrium

a physical state where an object is completely at rest and all the forces and turning forces acting on it are perfectly balanced

ex. hockey puck at rest on slippery ice

What is dynamic equilibrium

a state of a reversible process where the forward and reverse reactions happen at the exact same rate, causing no overall change to the system

ex. hockey puck sliding at constant speed on slippery ice (no acceleration and no friction/air resistance to slow it down)

What is the equilibrium test?

whether something undergoes change in motion

What causes acceleration

force; the amount you accelerate is proportional to net force

What does the force of friction depend on?

kind of materials and how they’re pressed together. this is due to tiny bumps on the surface and atoms attracting each other.

What is mass? (kg)

• how much material

• measure of inertia independent of gravity: more mass = more inertia

What is Newton’s Second Law of Motion

Newton's second law of motion states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass (F = ma)

What does an object falling through air experience?

force of gravity (downwards) and force of air resistance (upwards)

When does non free fall happen?

when air resistance is non-negligible

What does non free fall depend on

speed and surface area

What happens when air resistance equals gravity

terminal velocity; no more acceleration

What is Newton’s third law of motion?

Every action has an equal and opposite reaction

What is momentum?

property of moving objects; inertia in motion (mass x velocity)

What is impulse

overall effect of a force acting on an object over a period of time; force x time

What does impulse change

momentum; More impulse exerted = more change in momentum

How to increase momentum (ex. launching/striking an object)?

increase time of contact while pushing as hard as possible to maximize impulse

How to decrease momentum (ex. want slow)

increase time so impact force is smaller

What is the conservation of momentum

as long as there is no external forces, total momentum of interacting objects cannot change

What are elastic collisions

colliding objects rebound without lasting deformation or generating heat (not an everyday occurence)

What are inelastic collisions

colliding objects result in deformation and/or generation of heat (everyday occurences)

What is energy

Quantifies a system’s ability to do Work

• Observed when being transferred or transformed (always conserved)

What is work

Distance over which force is applied (joule)

What two things occur when work is done?

• A force acts on an object

• The object subject to the force moves

What is power

Measure of how fast Work is done (watt)

What is mechanical energy

total energy due to motion, position, or both

What are two forms of mechanical energy

kinetic energy and potential energy

What is potential energy

stored energy that has the potential to do work; due to relative position, electric charge, or internal stress

what is gravitational potential energy

due to an elevated position; work required to lift object (weight x height)

what is kinetic energy

Energy of motion of an object; Work required to bring from rest up to speed

What is thermal energy

kinetic energy of particles

What is mass-energy

form of potential energy

what is the work energy theorem

Any change in KE is the result of work

what is the conservation of energy

Energy cannot be created or destroyed; it may be transformed from one form to another, but the total amount of energy in the Universe stays the same

What is circular motion

Object rotates around an axis that passes through object

What kinds of speed is circular motion characterized by

tangential (linear) & rotational (angular)

what is tangential speed

The distance travelled by a point on a rotating object divided by the time taken to travel that distance

What points have higher tangential speed

points closer to the edge

What is rotational speed

the number of rotations or revolutions per unit of time

What is rotational inertia

Tendency to resist change to rotation

What does rotational inertia depend on

mass + distribution of mass; object’s shape + position of rotational axis

When is rotational inertia higher

objects with mass that is far away from axis of rotation

Greater the rotational inertia….

harder it is to change its rotational state

What is angular momentum

inertia of rotation

What is the conservation of angular momentum

If no external net torque acts on a rotating system, the angular momentum of that system remains constant.

What is torque

force used to change angular momentum; changes the rotational speed and momentum of an object

What does torque depend on

magnitude of force, direction of force, and where on object is force applied

What is centripetal force

Force directed towards center of a rotating object’s rotation (aka rotation axis)

• depends on: mass of object, tangential speed of object, radius of circle

What is centrifugal force

Away from center; Outward force we feel when rotating; push outwards

• can be used to simulate gravity

What is the universal law of gravitation

Every body attracts every other body

• Directly proportional to the product of their masses

• Inversely proportional to the square of the distance separating them

Inverse square law of gravity

gravitational force between two masses decreases as the distance squared between objects increases

How does gravity cause tides

• stronger gravity = closer to the ☾

• weaker gravity = farther from the ☾

• ☾ physically stretches earth; earth is slightly elliptical because of the ☾’s gravitational pull

• tidal bulge away and towards the ☾ (idk look at the slides for this)

how do the earth, ☾, and ☼ interact gravitationally without touching and being very far apart

through gravitational fields (region of influence)

What are gravitational fields at the center of a planet

Pull of the mass beneath partially counteracted by the pull from the mass above you

Gravitational pull outside of a planet?

Gravitational pull decreases as distance-squared

What is spacetime? (Einstein’s theory of General Relativity)

A gravitational field is a warping of space-time by any mass; warped space-time affects the motion of other object

Blackhole structure?

mass is contained at the very center in a singularity

• infinite density

• infinitely small

• finite mass

Black hole event horizon?

force of gravity strong enough that light cannot escape; outside light escapes while inside light is trapped

What is a projectile?

Any object that moves through air/space, experiencing gravity, continuing motion via inertia; combination of horizontal and vertical motion

What happens to projectile motion without gravity

straight path

What happens to projectile motion with gravity and no forward motion

fall straight down

What happens to projectile motion with gravity and forward motion

curved path

What is projectile motion if an object is only launched horizontally

the only force is downward gravitational force if you assume air drag is negligible. so the object will travel horizontally in equal distances in equal time periods

What is a parabola

Curved path with Constant acceleration in vertical and Moving horizontally at a constant speed

What happens when something is launched at different angles with the same force

horizontal motion will be the same but vertical motion will be different

Projectile motion at different angles regarding horizontal distance

• the same horizontal distance will be achieved if the angles add up to 90

• maximum horizontal distance achieved when thrown at a 45 degree angle (with air resistance)

maximum height without air resistance

the time for a projectile to reach maximum height is the same as the time for it to return to its initial level.

What is a satellite

a projectile that falls around Earth rather than onto it

A satellite in circular orbit regarding speed

• speed must be greater enough to ensure that its falling distance matches Earth's curvature

• speed is constant; only direction changes

• speed is unchanged by gravity

Positioning of circular satellite orbits

beyond Earth's atmosphere, where air resistance is almost totally absent

Motion of circular satellite orbits

moves in a direction perpendicular to the force of gravity acting on it

What does launching a payload into orbit require control over

• direction of rocket: fired vertically and then tips horizontally

• speed of rocket

What type of orbital path are most satellites

ellipses

What is Kepler’s first law of planetary motion

The path of each planet around the Sun is an ellipse with the Sun at one focus

What is Kepler’s second law of planetary motion

The line from the Sun to any planet sweeps out equal areas of space in equal time intervals

What is kepler’s third law of planetary motion

The square of the orbital period of a planet is directly proportional to the cube of the average distance of the planet from the Sun (for all planets)

PE and KE in circular orbit

steady speed and constant PE and KE because distance between the satellite and center of the attracting body does not change and no component of force acts along the direction of motion

PE and KE in elliptical orbit

KE is least when PE is the most and vice versa

• PE is greatest when the satellite is farthest away (apogee)

• PE is least when the satellite is closest (perigee).

What is all matter made up of

atoms

structure of atoms

neutrons, protons, and electrons in electron cloud

What is the probability cloud

general area of probability having an electron