fundamentals

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Created by
milena faulds

Cards (38)

  • Difference between speed and velocity -> One’s a scalar and one’s a vector.

    A scalar is a quantity or an amount, with no direction.
    A vector has both a quantity and a direction.

    speed -> how fast you’re going, no direction. so speed is a scalar.
    When you also have a direction, it’s a velocity.
  • Distance is a scalar and displacement is a vector.
    Acceleration is a vector because you speed up or slow down in a direction.
  • Mass doesn't have direction, so it’s a scalar. force does, so it’s a vector. Time and energy are scalars. Momentum and torque are vectors.
  • Vector addition
    Add vectors by drawing them head to tail. Tail of one vector to the head of the other vector. new arrow from leftover tail to leftover head is the resultant.
  • Vector subtraction
    add the opposite -> flip the second vector and then add it.
  • If you add (or subtract) vectors, and you get back to where you started, then the resultant is zero
  • Change in (Δ) = Final − Initial
  • example question
  • tanθ = o/a
    sinθ = o/h
    cosθ = a/h
  • vertical and horizontal components of ball travelling at 8ms-1^1
  • Conversion from radians to degrees
    Conversion from degrees to radians
  • units table
  • standard form: 230,000,000 = 2.3 ×108^8
  • ∝∝
    If two variables are proportional, then when one halves, so does the other. When onetriples, so does the other.

    If two variables are inversely proportional, then when one halves, the other doubles. When one triples, the other is divided by three.
  • A system is a collection of objects that you want to describe. You can choose what your system is.
    • Objects inside the system are internal and objects outside are external.
    • Forces from objects outside the system are called external forces
  • Centre of mass is (COM)
    Point you draw forces acting on things. Mass looks like its concentrated at the point. This is for one object.
  • COM of system with two objects
    xcom = m1x1 + m2x2 / m1 + m2
    x1 -> distance from reference point to object 1.
    x2 -> distance from reference point to object 2. x
    xcom -> distance from reference point to centre
    of mass
  • Example question -> reference point on top of object 1 x1=0

    formula changes to -> xcom=m2x2 / m1 + m
  • If COM moves, to figure out velocity of mass replace distance (x) with velocity (v) in COM equation.

    Vcom = m1v1 + m2v2 / m1 + m2
    =>
    total momentum of system / m1 + m2
  • If the total momentum of the system is conserved (i.e. is constant), then vcom is constant too.
    If there is an external force acting on the system, then total momentum changes, and v com changes too.
    The position of the COM only ever accelerates if
    there is an external force acting on the system.
  • Forces push and pull on objects. Unless they are cancelled out, forces cause acceleration. Forces are vectors, so we represent them with arrows in force diagrams. Force, mass and acceleration are connected: F = ma
  • Newtons laws

    First Law: When the net force on an object is zero, it stays at a constant velocity.
    Second Law: When the net force on an object is not zero, it will accelerate in the direction of that net force.
    Third Law: Every force has an equal and opposite force.
  • Forces are vectors, use the vector addition to find the
    net force -> the net force is the overall or total or resultant force
  • force example
  • support force
    Support forces are perpendicular (at a right angle) to the surface that’s doing the supporting.
    If the surface is flat, then the support force is straight upward. If the surface is a slope, then the force will be perpendicular to that slope.
  • tension force
    when a rope is under tension, it’s pulling something up and it’s pulling down from whatever it’s attached to. These forces are equal and opposite.
    Imagine tension as a force that acts toward the centre of a string or cable.
  • Mass vs Weight
    Mass is how hefty something is. Mass is measured in kilograms (kg).

    Weight is the force due to gravity. This is given by the equation
    Fg = m x g, m is mass and g is the acceleration due to gravity. Weight is measured in Newtons (N). 
  • Energy can be described as the ability to do work
    Energy can be changed from one type to another.

    Gravitational potential energy, elastic potential energy, and
    kinetic energy

    Energy is always conserved.
    You can’t create or destroy energy – you can only turn it from one type to another
  • The total energy of a system is always conserved. This consists of potential energy (gravitational or elastic) and kinetic energy. These can be converted into each other so long as the total EK+ EP is always the same number.
  • gravitational potential energy

    If something’s up high, then it could drop and gain kinetic energy. This potential energy is called gravitational potential energy.

    It’s calculated with this formula: EP= m x g x h, m is mass, g is gravity, h is height about reference point.
    Ep is measured in Joules (J)
  • Elastic potential energy

    If you stretch or compress a spring then it will unstretch or uncompress when let go. So it must have had potential energy before.

    Calculated with the formula EP =1/2kx2^2, k is the spring constant (in Nm−^-1^1) and x is the amount of stretching/compressing (in m)
  • Kinetic energy
    Energy objects have from moving. Two kinds: linear and rotational, measured in joules
    Calculated with: -> Ek(LIN) =1/2 x m x v2^2
    -> Ek(ROT) = 1/2 x I x ω2^2
  • Elastic collision

    The overall kinetic energy is the same before and after the collision.
    If a collision is elastic or no kinetic energy is lost, then Ek(initial)= Ek(final)
  • Inelastic collision
    Some kinetic energy is lost in the collision. Typically lost as heat energy. Assume collisions are inelastic. For inelastic collisions, Ek(initial)> Ek(final). While kinetic energy is not conserved, overall energy is conserved, because the lost kinetic energy becomes another type of energy, e.g. heat
  • Work

    Work (W) is the energy used up, in J, when moving an object over a distance with a
    force.
    Calculate with W = F x d, W is work done, F is force applied, d is displacement travelled
  • Momentum
    An object's linear momentum is calculated by p = m x v, P is momentum, m is mass, v is velocity

    momentum is a vector (has size and direction)

    Momentum is conserved if no external forces are applied. If no external forces then the total momentum of the system will be the same (any time or event), for example, a collision of two objects. Initial and final total momentums are equal: pi= pf
  • Frequency

    Frequency (f) is how many times the thing happens in one second. Measured in Hertz (Hz). Another way of writing Hz is s−^-1^1

    Calculated by f = 1/T
  • Period

    A Period (T) is the number of seconds it takes to do a thing. Periods are measured in seconds.

    Calculated by T = 1/f