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 MotionBalanced 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

v

rT

r

va

2

2

Periodic Motion

Kepler's three lawsPlanetary 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.

• Magnetized Material

• Unmagnitized 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 waterElectric 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 volt

Current = ------------ 1 ampere = 1 ------

resistance ohm

• How does the human body respond to electric currents?(see p.514)