TAKS Objective 5 Motion Forces and Energy Energy

TAKS Objective 5 Motion , Forces and Energy

Energy Is defined as the Ability to do Work Energy has 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 Will it fall? GPE = m g h 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 m = 95 kg g = 9. 8 B 64, 600 2 h =joules m/s 100 m C 93, 100 joules 2 x 100 95 Dkg 121, 600 x 9. 8 m/s joules = 93, 100 joules C

Law of Conservation of Energy ¢ Energy can change forms, but is never created nor destroyed ¢ 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.

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

Energy can be conserved in Non-Mechanical forms The chemical energy in a battery transforms into electrical energy Any reaction where more energy is given off than is used to start it is Exogonic An Endogonic reaction absorbs energy and causes cooling

Electrical Energy Moving electrons in a path is electricity ¢ ¢ ¢ Electrical Potential Difference (v) is measured in Volts 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).

Circuits – 2 types ¢ Series circuits are the most simple. ¢ 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)

Circuits – 2 types ¢ 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.

6. Which switches, if opened, will cause the light bulb to stop glowing? F. Q G. R It is the only H. S switch in J. T 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? A. 0. 22 amp V = I R so, B. 4. 5 amps C. 11. 0 amps 9 V = I x 2 ohms D. 18. 0 amps 4. 5 amps or

Thermal Energy A body contains internal KE due to the motion of its atoms ( they are constantly wiggling and jiggling) Thermal Energy is the total internal KE of a body Temperature is the average KE of a body

Heat- Transfer of Thermal Energy Three forms of heating: 1. Conduction-direct contact, a pot heating on a stove (solids) ¢ 2. Convection- heating by circulating fluids, (gas and liquid) heating from a fireplace ¢ And. . . ¢

3. Radiation – Transfer of Electromagnetic (E. M. ) Energy Objects are heated when exposed to infrared radiation ¢ The suns heats the earth by sending infrared radiation along with other forms of E. M. energy 3. 0 x 108 meters through empty space ¢

Heat moves by conduction in solids since the particles are close together and vibrate. . . 43 Heat convection occurs in gases and liquids. Heat convection does not occur in solids because solids are unable to — A absorb heat by vibrating B transfer heat by fluid motion C emit radiation by reflecting light D exchange heat by direct contact Solids do radiate heat to their surroundings

2 The primary way liquids and gases transmit heat is by the process of — F reflection G conduction H radiation J convection Fluid heat movement is convection. Fluid motion occurs in liquids and gases.

50 A solar heater uses energy from the sun to heat water. The heater’s panel is painted black to — Convection is movement of heat in fluid matter, heat loss Faimprove emission of–change infrared would be from a solid exterior Not G radiation Painting substance will not its conductivity theofheat loss by. It convection – That is. Gareduce property metals. would havecurrents to be infrared radiation made of Ha improve differentabsorption substanceofto change that: Not J J reduce the heater’s conducting properties Emission is giving off – we want to absorb: Not F

Nuclear Reactions Fusion occurs when two atoms combine to form a new element. The sun produces all of its energy through fusion. Two hydrogen atoms combine to form a Helium atom from the great gravitational forces and pressure in the sun’s core

Nuclear Reactions Fission is the splitting of nucleii of large atoms such as Uranium and Plutonium ¢ Produces large amounts of infrared radiation and other forms of E. M. Energy such as Gamma Rays ¢ Currently, it is the main form of Atomic Energy on Earth ¢

Radiant Energy or Electromagnetic Energy (EM) All radiant energy travels at 3. 0 x 108 m/sec in space ¢ Velocity of a wave = wavelength x frequency ¢ Visible light is just one type of EM Energy ¢

All of the forms of radiation given off Electromagnetic Spectrum by vibrating electric charges Radiation comes in the form of vibrating or “throbbing bundles of energy” called photons The frequency of the vibrating electric charges determines which type and how much energy will be given off

The entire E. M. Spectrum in order from lowest to highest frequency ¢ Radio waves: AM and FM ¢ Microwaves: cooking ¢ Infrared: heat ¢ Visible: (ROYGBV) ¢ Ultraviolet: tanning ¢ Xrays: medical ¢ Gamma:

Waves - Energy carried by rhythmic disturbances Two types: ¢ 1. E. M. radiation move through empty space ¢ 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 ¢ Amplitude – the size of the movement of the vibrating particles ¢ 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

And the answer is? J 3300 Hz 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 0. 0033 Hz Use the formula chart!!! G 33 Hz Velocity = f λ OR H 330 Hz J 3300 Hz 330 m/s = f x 0. 10 m

Transverse Waves ¢ 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

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

Sound Waves are Compression Waves Sound is produced when a compression is made. It requires a producer and a medium to travel through. The more elastic the object, the faster sound travels.

Sound acts like other waves ¢ Echoes are reflected sound waves ¢ Sonar uses echoes to judge distance to obstructions ¢ Human hearing is 2020, 000 Hz, below 10 Hz is infrasonic, and above 20, 000 Hz is ultrasonic.

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 — Resonance is the vibration F interference of another object struck by a G the Doppler effect wave of the correct frequency. Since the forks H resonance are identical, the second J standing waves one receives the correct frequency to begin vibrating.

Forces and Motion ¢ ¢ Forces can create changes in motion (acceleration) Deceleration is negative acceleration

Motion can be described as ¢a change in an object’s position ¢ Average velocity (speed) is the change of position of an object over time

Velocity Graphs V = distance time ¢ Velocity (v) is the slope (rise over run) of a position (d) vs. time (t) graph

40 The diagram represents the total travel of a teacher on a Saturday. Which part of the trip is made at the greatest average speed? FQ How do we work this one? GR Calculate v = d/t for each segment. HS J T

Acceleration Graphs Acceleration (a) is the slope of a velocity (v) vs. time (t) graph ¢ Plotted on a distance vs. time graph, acceleration is an exponential curve ¢

Acceleration is a change in an objects velocity (speed or direction) When an object’s speed changes over time it is accelerating (or decelerating) ¢ A = vfinal – vinitial time ¢ Units for acceleration m/s/s or m/s 2 ¢

Definition of a Force ¢ A Force is a push or a pull

Balanced Force ¢ A force that produces no change in an object’s motion because it is balanced by an equal, opposite force.

4 The picture shows the position of a ball every 0. 25 second on a photogram. Using a ruler, determine the velocity of the ball. F 3. 5 cm/s G 10. 5 cm/s H 14. 0 cm/s J 28. 0 cm/s

Use the ruler on the side of the chart and the equation for velocity. The answer was H. Measure from the center of ball 1 to the center of ball 2 and multiply by 4.

Unbalanced Forces Are forces that results in an object’s motion being changed. +

Friction A force that acts in a direction opposite to the motion of two surfaces in contact with each other.

Friction causes an object to slow down and stop. Since the amount of energy stays constant, the energy becomes heat.

Newton’s 1 st Law of Motion ¢ Object in motion stays in motion

Newton’s 1 st Law of Motion ¢And Objects at rest stay at rest

Newton’s 1 st Law of Motion ¢ Until they are acted upon by unbalanced forces.

Inertia or Newtons 1 st Law Tendency for an object to stay at rest or moving in a straight line at a constant speed. ¢ The mass (m measured in kg) of an object determines its inertia ¢

Newton’s 2 nd Law of Motion Force = Mass X Acceleration F=ma Weight (pull of gravity) is a commonly measured force, calculated by F=mg, g is the acceleration due to gravity 9. 8 m/s 2

Newton’s 2 nd Law of Motion The greater the mass of an object, the greater the force required to change its motion.

Newton’s 2 nd Law of Motion ¢ The greater the acceleration of an object, the greater the force required to change its motion.

11 The frog leaps from its resting position at the lake’s bank onto a lily pad. If the frog has a mass of 0. 5 kg and the acceleration of the leap is 3 m/s 2, what is the force the frog exerts on the lake’s bank when leaping? ¢ ¢ A 0. 2 N B 0. 8 N C 1. 5 N D 6. 0 N Formula chart says F=ma, m is mass in kg, a is acceleration in m/s 2. So, . 5 kg x 3 m/s 2= 1. 5 N

Newton’s 3 rd Law of Motion ¢ For every action force there is an equal and opposite reaction force.

Newton’s 3 rd Law of Motion All forces come in actionreaction pairs Ex: feet push backward on floor, the floor pushes forward on feet

27 A ball moving at 30 m/s has a momentum of 15 kg·m/s. The mass of the ball is — A 45 kg B 15 kg C 2. 0 kg Formula Page says that Momentum = Mass x Velocity D 0. 5 kg So 15 kg. m/s = M x 30 m/s solving for M it is:

Work: using a force for a distance ¢W=Fxd ¢ The work done by forces on an object = changes in energy for that object. ¢ Work and Energy are measured in Joules ¢ 1 Joule=1 Newton • meter ¢

42 How much work is performed when a 50 kg crate is pushed 15 m with a force of 20 N? F 300 J Use the formula Work = Force x distance G 750 J H 1, 000 J Force of 20 N x 15 meters = 300 Joules J 15, 000 J Answer:

Why use a machine? ¢ In an ideal (perfect) machine the work put into the machine (Win) = the work put out by that machine (Wout)

Machines make work easier The ideal mechanical advantage of a machine (IMA) of a machine is the number of times the output force is larger than the input force IMA=Fout/Fin ¢ A machine can only make this happen by moving the input force through a farther distance than the output force ¢ ¢ Fin • din=Fout • dout

48 The diagram shows an electric motor lifting a 6 N block a distance of 3 m. The total amount of electrical energy used by the motor is 30 J. How much energy does the motor convert to heat? F 9 J G 12 J H 18 J J 21 J

Work Input = 30 J done by the motor Work Output = Resistance Force x Resistance Distance Workout = 18 J = 6 N x 3 m The difference is lost as heat due to friction, which is 30 J – 18 J = 12 J Answer G

Real Machines use Energy No real machine is 100 % efficient. i. e. none put out more work than is put in ¢ Efficiency of a machine is work output/work input X 100 % ¢ ¢ Eff = Wout X 100% W in

Machines use power Power: the rate at ¢ which energy is used (work is done) ¢ P=Work/time ¢ Power is measured in H. P. or watts ¢ 1 watt = 1 Joule 1 sec

45 If a force of 100 newtons was exerted on an object and no work was done, the object must have — A accelerated rapidly B remained motionless C decreased its velocity D gained momentum Work = Force x Distance Work = 0 so Force = 100 N 0 J = 100 N x d distance must be 0 It did not move!

6 Types of simple machines ¢ Some Simple Machines: ¢ Inclined planes ¢ Screws ¢ Pulleys ¢ Wheel and axle ¢ Levers ¢ Wedge

Universal Law of Gravitation All objects in the universe attract each other by the force of gravity

Universal Law of Gravitation 1) the mass of the object doing the pulling, and Gravity varies depending on two factors: 2) the distance from the center of that object

On Earth gravity = 9. 8 m/s/s ¢For every second that an object falls its speed increases by 9. 8 m/s

Weight= Mass (m) X gravity (g) ¢ Weight Unit of mass = kg ¢ Unit of acceleration = m/s/s ¢ Unit of weight = Newton ¢ 1 Newton= about ¼ pound

USE THE FORMULA PAGE. 0 0 0 1 1 1 2 2 2 3 3 3 4 4 4 5 5 5 6 6 6 7 7 7 8 8 8 9 9 9 Some of the problems require you to grid in an answer. Make sure you pay attention to the decimal point in the square in the middle.