TAKS Physics Review DAY 1

Objective 5 - Physics Force and motion Force and motion Newton’s laws Newton’s laws Waves Waves Conservation of energy Conservation of energy Heat transfer Heat transfer Electrical circuits Electrical circuits Simple Machines Simple Machines

Motion: Speed Speed (S) - a distance traveled in a given amount of time. Speed (S) - a distance traveled in a given amount of time. LOOK at the formula on your chart: LOOK at the formula on your chart: Speed = Distance Traveled Time In other Words: Speed is just the distance traveled over time.

Speed Example: I.4A 10 th Spring 2003 First let’s list what we know and what we want to find out. We know: Distance traveled= 150 km Time =2.5 Hours We want to find out: ??Average speed???

So what is the difference between speed and velocity? Velocity is the vector quantity of speed. Velocity is the vector quantity of speed. Remember: a vector needs to have a magnitude and direction. Therefore: Velocity is just the speed (magnitude) in a given direction. Let’s come up with some examples!!!

Motion: Acceleration When an object's velocity changes, it accelerates. Acceleration shows the change in velocity in a unit time. When an object's velocity changes, it accelerates. Acceleration shows the change in velocity in a unit time. Let’s look at the formula: Acceleration = final velocity – initial velocity change in time In words: Acceleration is just the change of velocity over a period of time.

Example A roller coaster has a velocity of 3 m/s and an acceleration of 15 m/s 2. How many seconds will it take the roller coaster to reach its maximum velocity of 27 m/s?

First let’s list what we know and what we want to find out. We know: The current (or initial) velocity: 3 m/s, v i The acceleration: 15 m/s 2, a The maximum (or final) velocity: 27 m/s, v f We want to find out how much time it will take the roller coaster to accelerate from 3 m/s to 27 m/s.

We need to solve for time so we need to rearrange our formula and solve for change in time. First: acceleration x change in time = final velocity – initial velocity Then solve for time: change in time = final velocity – initial velocity acceleration SOLVE IT!!!

Motion: Momentum Objects in motion are said to have a momentum. This momentum is a vector. It has a size and a direction. momentum is equal to the mass of the object multiplied by the object's velocity. The direction of the momentum is the same as the direction of the object's velocity. From our formula chart: Momentum = mass x velocity

Momentum Momentum is a conserved quantity in physics. Momentum is a conserved quantity in physics. One object might change momentum, say losing some momentum, as another object changes momentum in an opposite manner, picking up the momentum that was lost by the first. One object might change momentum, say losing some momentum, as another object changes momentum in an opposite manner, picking up the momentum that was lost by the first. ρ 1 = ρ 2 therefore m 1 v 1 = m 2 v 2

Example 7. The 500 g cart is moving in a straight line at a constant speed of 2 m/s. Which of the following must the 250 g toy car have in order to maintain the same momentum as the cart? F An acceleration of 5 m/s2 for 2 seconds G A potential energy of 20 J H A constant velocity of 4 m/s J An applied force of 5 N for 5 seconds

Newton’s Laws Newton's First Law of motion (Law of Inertia) An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force. An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force. unless acted upon by an unbalanced forceunless acted upon by an unbalanced force

Newton’s Laws cont. Newton's second Law of motion (Law of acceleration) The second law states that the acceleration of an object is dependent upon two variables – The second law states that the acceleration of an object is dependent upon two variables – the net force acting upon the net force acting uponnet forcenet force the object and the mass the object and the mass of the object. of the object.

Newton’s Laws cont. Newton's third Law of motion (Law of action and reaction) (Law of action and reaction) For every action, there is an equal and opposite reaction For every action, there is an equal and opposite reaction

Back to our Formula Chart Force - a push or a pull on an object that will result in the acceleration of the object. F = ma Force - a push or a pull on an object that will result in the acceleration of the object. F = ma Force is measured in Force is measured in NEWTONS (N) NEWTONS (N) A newton is simply a A newton is simply a kg*m kg*m s 2 s 2

Formula Chart contd. Work - occurs when a force causes an object to move in the direction of the force W=Fd W=Fd Work is measured in JOULES (J) JOULES (J) A joule is simply a newton*meter

Formula Chart cont. Power - The amount of work that gets done over a certain amount of time. P= W_ t Power is measured in WATTS (W) WATTS (W) A watt is simply a joule A watt is simply a joule s

Formula Chart cont. %efficiency is simply the relation of how much work are you getting out related to how much work you actually put into a process. From our chart: %efficiency = work output %efficiency = work output work input work input X 100

Sample Problems 1. You must exert a force of 4.5 N on a book to slide it across a table. If you do 2.7 J of work in the process, how far have you moved the book? a..30 m b..79 m c..60 m d. 1 m

Sample Problems cont.

Energy Is defined as the Ability to do Work There are two Types: Kinetic (Energy of Motion) and Potential (Stored Energy)

Kinetic Energy KE = ½ m v 2 Ex: A moving car has the ability to do work on the light pole if it hits it.

Potential Energy 2 possibilities Gravitational PE -Object lifted to some height Elastic PE - A stretched or compressed object (spring or rubber band)

Gravitational Potential Energy or Wi ll it fall? GPE = m g h m is the mass of the m is the mass of the object in Kg, g is the acceleration due to gravity which is 9.8 m/s 2 on earth and h is the height in meters

Use the formula page! PE = mgh 41 What is the potential energy of the rock? A 59,900 joules B 64,600 joules C 93,100 joules D 121,600 joules m = 95 kg g = 9.8 m/s 2 h = 100 m 95 kg x 9.8 m/s 2 x 100 = 93,100 joules C

Law of Conservation of Energy Energy can change forms, but is never created nor destroyed Energy can change forms, but is never created nor destroyed Loss in one form = gain in an another form Loss in one form = gain in an another form A falling object speeds up as it falls to the ground; PE decreases as KE increases. The KE it has at impact = the PE it had before it fell. A falling object speeds up as it falls to the ground; PE decreases as KE increases. The KE it has at impact = the PE it had before it fell.

Example: A falling object speeds up as it falls to the ground; PE decreases as KE increases, the KE it has at impact with the ground is equal to the PE it had before it fell

Sample Problems

Sample Problems cont.

36

PHYSICS REVIEW DAY 2

Waves - Energy carried by rhythmic disturbances Two types: Two types: 1. E.M. radiation move through empty space 1. E.M. radiation move through empty space 2. Mechanical require a medium (air, water or any type of matter) for movement 2. Mechanical require a medium (air, water or any type of matter) for movement

Waves - 2 Types

All waves have similar properties Frequency- the number of vibrations per second or the speed of the movement of the vibrating particles Frequency- the number of vibrations per second or the speed of the movement of the vibrating particles Amplitude – the size of the movement of the vibrating particles Amplitude – the size of the movement of the vibrating particles Both are controlled by the disturbance that created the waves Both are controlled by the disturbance that created the waves

Velocity of all waves - v=f λ f-frequency and λ is wavelength (distance between identical points on two consecutive waves) Reflection- bounce off barriers in regular ways Refraction- waves can change direction when speed changes

The speed of a wave is the distance the wave travels in one unit of time. The speed of a wave is measured in units per second (m/s). A waves velocity is its speed in a particular direction. Frequency is a measure of how many wavelengths pass a particular point in one unit of time. Measured in hertz (hz). One hertz is equal to one wave per second. -So, if four complete wavelengths pass you every second, the frequency is four waves per second, or four hertz.

And the answer is? 38 At 0°C sound travels through air at a speed of 330 m/s. If a sound wave is produced with a wavelength of 0.10 m, what is the wave’s frequency? F Hz G 33 Hz H 330 Hz J 3300 Hz Use the formula chart!!! f λ OR Velocity = f λ OR 330 m/s = f x 0.10 m J 3300 Hz

Transverse Waves In Transverse Waves particles vibrate at right angles to the direction the wave travels. In Transverse Waves particles vibrate at right angles to the direction the wave travels. Ex. E. M. Waves, waves on a slinky or rope coil, ocean waves Ex. E. M. Waves, waves on a slinky or rope coil, ocean waves

Longitudinal or Compress ional Waves Vibrating particles move back and forth along the direction of the wave velocity Parts consist of compressions and rarefactions Ex. Sound Waves

Sample Problem

Sound Waves move through matter not through empty space. 32 One tuning fork is struck and placed next to an identical fork. The two forks do not touch. The second tuning fork starts to vibrate because of — F interference G the Doppler effect H resonance J standing waves Resonance is the vibration of another object struck by a wave of the correct frequency. Since the forks are identical, the second one receives the correct frequency to begin vibrating.

Heat Transfer Difference between Heat and Temperatute. Difference between Heat and Temperatute. Heat is energy that is transported from warmer objects to colder objects. Temperature is a measure of the amount of kinetic energy and momentum atoms and molecules have in an amount of gas, liquid, or solid.

transfer of heat through a SOLID, where kinetic energy is transferred from molecule to molecule transfer of heat through a SOLID, where kinetic energy is transferred from molecule to molecule Objects MUST touch Objects MUST touch –THINK of a CONDUCTOR

Convection: transfer of heat that occurs from the motion of fluid in LIQUID or GAS that is caused by differences in temperature Convection: transfer of heat that occurs from the motion of fluid in LIQUID or GAS that is caused by differences in temperature

transfer of heat by electromagnetic WAVES that are produced by thermal motion of molecules and atoms transfer of heat by electromagnetic WAVES that are produced by thermal motion of molecules and atoms SUN!!! SUN!!! NO TOUCHING NO TOUCHING

Sample Problems

Sample Problems cont.

Electrical Energy - Moving electrons in a path is electricity Electrical Potential Difference (v) is measured in Volts Electrical Potential Difference (v) is measured in Volts The rate of moving electric charges, Electric Current (I), is measured in Amperes The rate of moving electric charges, Electric Current (I), is measured in Amperes Resistance or opposition to the movement of the energy is called Resistance (R). Resistance or opposition to the movement of the energy is called Resistance (R).

Circuits – 2 types Series circuits are the most simple. Series circuits are the most simple. One (1) path for the current to travel. One (1) path for the current to travel. Contains an energy source, a path, and a load (something for it to do, like a lamp) Contains an energy source, a path, and a load (something for it to do, like a lamp)

Circuits – 2 types Parallel circuits provide more than one path for the current to travel. Parallel circuits provide more than one path for the current to travel. Most circuits are parallel, since if one lamp goes out, the others can stay lit. Most circuits are parallel, since if one lamp goes out, the others can stay lit.

F. Q G. R H. S J. T 6.Which switches, if opened, will cause the light bulb to stop glowing? It is the only switch in series to both the battery and light.

USE THE FORMULA SHEET!! What is the current in a copper wire that has a resistance of 2 ohms and is connected to a 9 volt electrical source? What is the current in a copper wire that has a resistance of 2 ohms and is connected to a 9 volt electrical source? A amp B. 4.5 amps C amps D amps V = I R so, 9V = I x 2 ohms or 4.5 amps

Remember Use your Equation Sheet Use your Equation Sheet Use your Calculator Use your Calculator Use your Periodic Table Use your Periodic Table