S2 Final Exam Review
Newton's First Law of Motion
There are two parts to
this statement – one
which predicts the
behavior of stationary
objects and the other
which predicts the
behavior of moving
objects. These two
parts are summarized
in the following
diagram:
Newton's Second Law of Motion
Newton’s Third Law: Action-Reaction
According to Newton's third law, for every action
force there is an equal (in size) and opposite (in
direction) reaction force. Forces always come in
pairs — known as "action-reaction force pairs."
Newton's First Law of Motion
Balanced and Unbalanced Forces
Friction Force
• Friction acts in opposite direction of applied force.
• Friction force increases as normal force increases.
• Friction caused by molecular interaction between two
rough surfaces.
Ffriction = μ x Fnorm
• μk = coefficient of kinetic friction
• μs = coefficient of static friction
Component Vectors
Component Vectors
Also see Sample Problem 3-2 (p.35)
Inclined Plane
Torque
60 kg.
?? Kg.
Uniform Circular Motion
• A particle in uniform circular
motion travels around a circle
or a circular arc at constant
speed.
• The particle is accelerating!
• It’s accelerating inward
(centripetal acceleration)
• The time for a particle to go
around a closed path is the
period of revolution
v2
a
r
2r
T
v
Periodic Motion
Kepler's three laws
Planetary Orbits.
Orbit simulator
Newton’s Law of Gravity
Momentum
• Momentum is simply how difficult it is to stop a moving
object.
• Momentum = mass x velocity or p=mv
• Change in momentum = mass x change in velocity, or
Δp = m . Δv
• The SI unit for momentum is kg.m /s
Impulse
• Impulse: the product of the force exerted on an object
and the time interval during which it acts.
• Impulse = Force . Elapsed time or J = F.Δt
• The SI unit for impulse is N.s
• Change in momentum = impulse! Sooo……
• F.Δt = m.Δv (known as the impulse-momentum
relationship)
Systems
1. Closed system – does not gain or loose mass
2. Internal force – force within a closed system
3. External force – force outside a system
4. Isolated system – when net external forces
equals zero.
Collisions When Two Objects Are Moving
When two objects collide they exert and opposite forces on each
other so the impulses cancel.
Systems can contain any number of objects:
– They can stick together or come apart
– The momentum of any closed system with no net external
force does not change.
Energy
Types of Energy: thermal, chemical, motion,
gravitational -- (units are Joules, J)
1 joule = 1 J = 1kg m/s2
Energy: the ability to produce change, in itself or
the environment
“the ability to do work”
Kinetic energy, K, is energy associated with a state
of motion of an object.
K=½ mv2
Let’s review Work
• Work is putting force on something over a
certain distance.
• Work = Force x distance = F x d
– Units is Joules
– e.g. Barbell, weight lifting
• 2x weight → 2x the work
• 2x weight and 2x distance → 4x the work
• What’s Power?
Power
• Power is work done on something for a
period of time.
• Power = work / time
– Units are in Watts (J/s)
• Does a car hoisted for lubrication in a
service station require work? Power?
– How does work change its energy?
– If we lift it twice as fast, does it require more
work or power?
Potential Energy
• Potential energy (U): energy
that can be associated with the
configuration (or arrangement)
of system of objects that
influence one another.
– Gravitational potential
energy, Ug
– Elastic potential energy, Ue
• ΔU = - W
• Ug = mgh
•
Mechanical Energy – the energy an
object possesses due to its motion or
position
•
Kinetic Energy – the energy due to its
motion.
•
Potential Energy – the energy due to
position
• Kinetic Energy – the energy due to its motion.
• Potential Energy – energy due to position
If you have a ball and put a constant force on it,
what type of energy is gained?
Kfinal = Work + Kinitial
p.250, practice problem
Atomic to Life Size?
• Magnetic domains
can be encouraged to
line up to form a
magnet.
• Unmagnitized Material
• Magnetized Material
Charging an object
• Induction – charging of an object without
direct contact.
• Friction – electrons transferred by friction
(ripped off the material)
• Conduction – electrons transferred by
direct contact with out friction.
Coulomb’s Law
Electric Fields and Potential
• An electric field fills the space around every electric
charge (remember gravity field?)
• The field is strongest where it would exert the
greatest electrical force on a charge.
• The direction of the field at any point is the direction
of the electric force on a positive charge.
• An electric field can be represented by electric field
lines
Electric Field Lines representation around a
negative charge.
(a) Vector representation
(b) lines-of-force representation
Electric Potential
Electric potential = electric potential energy
charge
The SI unit for electric potential is the volt (V)
1 volt = 1 joule / coulomb
Understanding Electricity - an analogy with water
Electric Current
• Electric current is simply the flow of electric charge.
• Flow: Water flow can be measured in many units but we
are using feet, so let's keep to cubic feet per second to
measure flow rate. The electrical equivalent is Amperes
(amps).
• Units: amperes (A).
• 1 A = 1 Coulomb / 1 sec
Ohm’s Law
• Georg Simon Ohm tested different wires in circuits to
see what effect the resistance of the wire had on current
voltage
Current = -----------resistance

volt
1 ampere = 1 -----ohm
• How does the human body respond to electric currents?
(see p.514)