With the absence of air resistance: the idealized motion is called free-fall and the
acceleration of a freely falling body is called the acceleration due to gravity near
surface of the earth. All of the free fall objects withstand the same downward
acceleration towards earth’s center.
Relative Motion: “Frame of Reference” is a coordinate system plus a timer
Velocity of Passenger Relative to Ground = Velocity of Passenger relative to train +
Velocity of the relative to ground.
V PGV + VPT TG
The two dimensional motion uses the vector addition / subtraction.
ΔV = V f V ]i The velocity change (speed / direction)
A =ΔV / Δt
While the instantaneous acceleration is defined as the limit as Δt approaches 0 of
ΔV / Δt
V a/b V a/t V t/bhere: a = person, t = transportation , b = motion of another
Uniform Circular Motion
V = 2πr / T where T represents the time elapsed, r = radius from the
center, and v = the velocity accelerating towards the center of the circle
The speed in a uniform circular motion is always constant.
ΔV / V = v Δt / r ΔV/ Δt = v / r
Therefore: a centripital/ r
*As the acceleration aims towards the center, the V tangentlways changes
throughout the motion Newton’s Law of Motion and their Application
Classes of forces: Contact / Field Forces; Consist of Force and Mass
Net force: the vector sum of all the forces acting on an object, written as ΣF.
Directed by the free body diagram.
Fx= F Cosθ
Fy= F Sinθ
F = -k s: a restoring force that exerts in the opposite direction of force applied
K is the spring constant
S is the change in the length caused by shift of the spring’s natural length
- Represents the negative displacement by a stretch
A force exerted in the opposite direction to the surface of the contact.
*Can also be a representation of the pressure between the surfaces of any two
It is a force between the surfaces of any two objects in the direction that
opposes the motion.
μ represents the friction constant.
Weight is always considered : mg
Newton’s Law of Motion
An object continues in a state of rest or in a state of motion at a constant
speed along a straight line, unless compelled to change that state by a net
force – forces on the object.
o ΣF=0, therefore, acceleration = 0 -> V constant
Inertial frame of reference; FoR when @ constant velocity
Inertial Mass: m of object is a quantitative measure of inertia
M inversely proportional 1/a; m1/m2 = a2/a1
The net external force, ΣF, acts on an object of mass m, results in an
acceleration, a, that:
o Directly Proportional to the ΣF
o Has a magnitude inversely proportional to the m
o The direction of the acceleration is the same as the direction of the
acting ΣF Therefore: a = ΣF / m
*When the velocity of a body is constant / at rest: It’s at Equilibrium