Physics for Life Sciences

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Physics for Life Sciences
2013-05-11 18:48:55
Massey 2013

1st year Physics
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  1. Prefixes tera to pico
    • tera T 1012
    • giga G 109
    • mega M 106
    • kilo k 103
    • hecto h 102
    • deka d 101
    • deci d 10-1
    • centi c 10-2
    • milli m 10-3
    • micro μ 10-6
    • nano n 10-9
    • pico p 10-12
  2. What is meant by significant figures
    • The figures of a number that express a magnitude to a specified degree of accuracy, rounding up or down the final figure.
    • 3.14159 to four significant figures is 3.142
  3. Know the SI units
    • Length m metre
    • Times s second
    • Mass kg kilogram
  4. Unit Conversion
    • 1 cm = 0.3937 inches
    • 1 m = 39.37 inches
    • 1 km = 0.6214 miles
    • 1 L = 1,000 ml = 1,000 cm3
    • 1 km/hr = 0.278 m/s = 0.621 miles/hr
    • 1 m/s = 3.6 km/hr = 2.237 miles/hr
    • 1 radian (rad) = 57.30°
    • 1° = 0.01745 rad
    • 1 rev/min (rpm) = 0.1047 rad/s
    • 1 W = 1J/s
    • 1 Pa = 1 N/m2
    • 1 day = 8.64 x 104 sec
  5. Pythagoras, SOCAHTOA
    The theorem that in a right angled triangle, the square of the length of the hypotenuse equals the sum of the squares of the other two sides

    • sin = opposite/hypo
    • cos = adjacent / hypo
    • tan = opposite /adjacent
  6. Displacement
    The displacement of an object is the change in position of the object

    Velocity: a measure of the rate of motion of a body expressed as the rate of change of its position in a particular direction with time, m/s

    Acceleration: the rate of increase of speed or the rate of change of velocity, a
  7. Average vs instantaneous velocity & acceleration
    • An object's average velocity over a particular time interval, Δt, is its
    • displacement Δx during that time interval, divided by Δt

    The instantaneous velocity is the average velocity taken over an infinitesimally short time interval

    An object's average acceleration over a time interval Δt is Δv/Δt

    Instantaneous acceleration is the average acceleration taken over an infinitesimally short time interval
  8. Kinematics equations
    • v = vo + at
    • x = xo + vot + ½at2
    • v2=vo2 +2a(x-xo)
    • average v=(v + vo)/2
  9. Newton's Laws of Motion
    Every object continues in its state of rest or of uniform velocity in a straight line as long as no net force acts on it

    The acceleration of an object is directly proportional to the net force acting on it and is inversely proportional to its mass. The direction of the acceleration is in the direction of the net force acting on the object. ΣF=ma

    Whenever one object exerts a force on a second object, the second exerts an equal force in the opposite direction on the first
  10. Weight
    Normal force
    Elastic force
    The magnitude of the force of gravity on an object is commonly called the object's weight

    When a contact force acts perpendicular to the common surface of contact, it is referred to as the normal force

    • When two objects slide over one another, the force of friction that each object exerts on the other can be written approximately as Ffr = μKFN, where FN is the normal force and μK is the coefficient of kinetic friction.
    • If the objects are at rest relative to each other, then Ffr is just large enough to hold them at rest and satisfies the inequality FfrsFN, where μs is the coefficient of static friction
    • When a flexible cord pulls on an object, the cord is said to be under tension, and the force it exerts on the object is the tension FT

    • The normal force is an elastic force caused by the deformation of the surface
    • Tension force: another elastic force caused by the stretching of the rope, rod, or spring or whatever it is
  11. Problem solving
    • Read and reread written problems carefully
    • Draw an accurate picture or diagram of the situation
    • A separate FBD needs to be drawn for each object involved, and it must show all the forces acting on a given object (and only that object)
    • Choose a convenient xy coordinate system (one that makes your calculations easier, such as one axis in the direction of the acceleration)
    • When using Newton's second law, apply ΣF = ma separately to x and y components, remembering that x direction forces are related to ax, and similarly for y
    • More generally, it may help to see if one or more relationships (or equations) relate the unknowns to the knowns
    • Use your intuition, and make rough calculations
    • Solve the problem, which may include algebraic manipulation of equations and/or numerical calculations
    • Be sure to keep track of units for they can serve as a check (they must balance on both sides of any equation)
    • Again consider if your answer is reasonable