Physics Notes Exam: May 6 2013
Displacement = distance travelled in specific direction, ‘net’ distance travelled from
certain position (p). Measured in m. Vector Quantity, (s)
Velocity = change in displacement per change in time (delta s / delta t). Measured in
ms. Vector Quantity:
o V = final velocity
o U= intial velocity
Acceleration = change in velocity per change in time (delta v/delta t). Measured in
ms . Vector Quantity (a)
Free Fall Motion
Acceleration is constant in free fall with an accelerating force of: 9.81ms
Air resistance is also a factor, as you accelerate downwards, obviously your
velocity will increase. As your velocity increases, so will the resistance of the air
until a point where the resistance is so high, that you will cease to accelerate
and maintain a uniform velocity. This is known as terminal velocity.
Graphical Representation of motion
Gradient of displacement line = velocity
Tangent to a point on S-graph = Instantaneous velocity
Gradient of Velocity line=acceleration
Area under velocity graph = displacement
Area under acceleration graph = velocity
Forces and Dynamics
o Normal Force
o Upthrust (buoyancy)
o Air Resistance
o Gravitational Force (W=mg)
o Friction Free Body Diagrams
o Diagrams showing forces acting on a body.
o Adding forces = adding x components, adding y components
o Balanced forces = no force = inertia = constant velocity = x components
are equal and opposite, same with y components.
Newton’s Laws of Motion
Newton’s First Law – Inertia
o All forces are balanced.
o Things that are in motion stay in motion, things that are in rest stay in
rest. By motion, I mean constant velocity. They stay like this until acted
upon by an external force.
o Translational Equilibrium = when all forces are balanced.
Momentum (p), N s, kg m s
o Rate of change in momentum (delta p / t) proportional to F
o Vector Quantity, therefore, momentum going one way doesn’t equal
momentum going the other way.
o Law of Conservation of Momentum
Momentum is always conserved, therefore, a bomb intact has
the same momentum as the sum of its particles when it
explodes. Because momentum is a vector quantity, the ‘net’
momentum equals zero.
Change in momentum
Newton’s Second Law – F = ma
o = Force
o ma = force
o Force is equal to mass x acceleration.
Newton’s Third Law
o Action vs. Reaction
o If a body A exerts a force on another body, B, body A will experience an
force equal and opposite from body B
o Just because the forces are equal and opposite, doesn’t mean each
body will be in balance as far as the forces go, because the forces are
acting on different objects.
o Conservation of momentum helps in determining the new velocities of
bodies after they collide.
o Momentum before must equal momentum after
o Different scenarios:
Bodies stick together - mu = (m + M)v Colliders hit each other but separate