Science Standards Review: Energy
S8P2. Students will be familiar with the forms and transformations of energy. a. Explain energy transformation in terms of the Law of Conservation of Energy.
The law of conservation of energy states that: • Energy is never destroyed • Energy is never created • Energy may be transformed or converted from one form to another • Energy is constantly changing forms
b. Explain the relationship between potential and kinetic energy. • Kinetic Energy • Energy of Motion • Depends on • Speed • Mass • More speed = more KE • More mass = more KE
Potential Energy • Energy of position (stored energy) • Gravitational PE depends on • Weight • Height • More weight = more PE • More height = more PE
c. Compare and contrast the different forms of energy (heat, light, electricity, mechanical motion, sound) and their characteristics.
Forms of Energy: Heat(thermal)—the vibration and movement of the atoms and molecules within substances ex. Atoms move faster in hot water vs. ice water Light (radiant)—is electromagnetic energy ex. Sunlight, X-rays, microwaves, p.636 Electricity—energy of moving electrons, typically moving through a wire ex. lightening
Sound—energy caused by an object’s vibrations Mechanical Motion—is energy stored in a moving object or an object that can move PE + KE = mechanical energy ex. Wind, Jack in the Box
Chemical—energy stored in the bonds of atoms and molecules (is released during chemical changes when atoms are rearranged) ex. Cells in our body store chemical energy Nuclear—energy stored in the nucleus of an atom — the energy that holds the nucleus together ex. Nuclear power plants http://www.eia.doe.gov/kids/energy.cfm?page=about_forms_of_energy-basics http://www.bbc.co.uk/schools/ks2bitesize/science/physical_processes/
d. Describe how heat can be transferred through matter by the collisions of atoms (conduction) or through space (radiation). In a liquid or gas, currents will facilitate the transfer of heat (convection).
Conduction is the transfer of energy through matter from particle to particle as they touch. • Transfer of heat energy from atom to atom • Most effective in solids. • Heat moves from warmer substances to cooler substances.
Convection the transfer of thermal energy by the movement of a gas or liquid (a medium). The circular motion caused by density differences that result from temperature differences are called convection currents.
Radiation • the transfer of thermal energy by • electromagnetic waves such as visible light • and infrared waves. (See p. 636-637). • This energy can be transferred through • particles of matter OR empty space! Examples Energy from the sun Microwaves use radiation
Review Questions Which of the following converts electrical energy into mechanical? A light switch B electric stove C light bulb D electric fan
According to the Law of Conservation of Energy, if Sally throws a watermelon with 100 joules of energy off the roof of a building, how much energy should the watermelon have as it hits the ground? • 200 joules B. 150 joules • C. 100 joules D. 0 Joules
When a rock is thrown straight up into the air, it reaches its highest point and briefly comes to a complete stop before it starts to fall back to the ground. Which is greatest at the point where the rock stops? • A. potential energy • B. kinetic energy • C. force due to gravity • D. friction
A house becomes warm after air circulates in the house. What type of heat transfer happens? Conduction Convection Radiation
Why do we insulate our soda cans? • To keep heat in • To keep heat out • To keep cold in • To keep cold out
Where is kinetic energy the greatest? A B C D Where is potential energy the greatest? A B C D
Tonya drops a ball off a cliff as shown in the picture. Which position shows where the ball has the most kinetic energy and the least potential energy? A) A B) B C) C
Bob sat by the pool too long and his skin began to burn. What type of heat transfer occurred to make him burn? Conduction Convection Radiation
At which position in the pendulum swing is kinetic energy greatest? a. A b. B c. C d. D At which position in the pendulum swing is potential energy the lowest? a. A b. B c. C d. D
What type of heat transfer is happening in the picture? A. Heat to electrical B. Chemical to mechanical C. Mechanical to light D. Heat to mechanical What type of heat transfer is happening in the air around the candle? Conduction Convection Radiation
A gasoline-powered vehicle goes up a hill from point X to point Y. What energy transformation must occur in the car’s engine? A Chemical energy into mechanical energy B Electrical energy into light energy C Electrical energy into sound energy D Mechanical energy into light energy
When walking along an asphalt street after sundown, a person often feels heat coming off the pavement. The heat is moving from the asphalt to the person by • A. Conduction B. convection • C. Expansion D. radiation Heat, light, and electricity are all forms of • A. Atoms B. energy • C. Cells D. motion
The batteries in a flashlight make electricity using • A. chemical B. solar • C. heat D. mechanical In the pictures below, the candle is heating the water in the tank. Which picture shows how the water will move as it gets hot?
My dog, Ralph, wears slippers on hot days because the pavement is hot on his feet. What type of heat transfer makes his feet hot? Conduction Convection Radiation
S8P3. Students will investigate relationship between force, mass, and the motion of objects. a. Determine the relationship between velocity and acceleration.
Velocity— • the speed of an object in a particular direction • velocity must include speed (distance over time) anddirection! • ex. an airplane travels west at 600 km/h • if speed or direction changes the velocity changes
Practice: Tom is traveling west at 50 miles per hour. Sally and her family are traveling south at 50 miles per hour. Do the cars have the same velocity? Why or why not? Tom Sally
Acceleration— • The rate at which velocity changes • An object accelerates if its speed or • direction changes • an increase in velocity is called positive • acceleration • a decrease in velocity is called negative • acceleration or deceleration • the faster the velocity changes, the greater • the acceleration
b. Demonstrate the effect of balanced and unbalanced forces on an object in terms of gravity, inertia, and friction.
Balanced Forces • Occur when the forces on an object • produce a net force of 0 Newtons (N) • Will not cause a change in the motion of a • moving object • Will not cause a nonmoving • object to start moving • ex. Hat on your head, bird’s nest
Unbalanced Forces • Occur when the net force on an object is • not 0 Newtons (N) • The forces are unbalanced • Produce a change in motion • Are necessary to start movement or • change movement • ex. kicking a ball
Decide whether the following pictures represent a balanced or unbalanced force
Gravity— • A force of attraction between objects due • to their masses • Law of Universal Gravity—all objects in the • universe attract each other through • gravitational force + Yes, you really are attracted to your science book!
a. Recognize that every object exerts gravitational force on every other object and that the force exerted depends on how much mass the objects have and how far apart they are.
Gravity decreases as distance increases. • The more mass, the more • gravitational force
Inertia— • The tendency of objects to resist any • changes in motion • The more mass the more inertia More mass more inertia Less mass less inertia
Friction— • A force that opposes motion between two • surfaces that are in contact • Can cause a moving object to slow down • and eventually stop • Caused by roughness of surfaces
c. Demonstrate the effect of simple machines (lever, inclined plane, pulley, wedge, screw, and wheel and axle) on work.
Inclined Plane— • A flat slanted surface • Less input force necessary, but must be exerted over a longer distance • Examples: ramps, stairs,
Wedge— • Device that is thick at one end and tapers to a thin edge at the other end (two inclined planes back to back) • The longer and thinner the wedge, the less input force is required (same as with the inclined plane) • Examples: End of an ax, knife, zipper, • Push pin
Screw— • An inclined plane wrapped around a cylinder • The closer the threads, the greater the mechanical advantage (longer distance, but less input force needed) • Examples: Jar lid, bolts, faucets The closer the threads the greater the mechanical advantage
Wheel and Axle— • Two circular objects fastened together that rotate about a common axis • The object with the larger diameter is the wheel and the object with the smaller diameter is the axle • Multiplies your force, but you must exert your force over a longer distance • Examples: door knobs, steering wheels, screw drivers wheel axle
Levers— • A rigid bar that pivots or rotates about a fixed point called a fulcrum 3 different classes (types) of levers • 1) 1st Class Levers— • Fulcrum (pivot point) is located between the input and output force (the load). • Change the direction of the force (they can also change size or distance of the force) Examples: Seesaw, scissors, pliers, catapult Effort Load Effort Fulcrum Fulcrum Output/load
2nd Class Levers— • The load is between the fulcrum and input force (effort) • Do not change the direction of the input force • You must exert less force over more distance • Examples: Bottle openers, wheelbarrows Input force (effort) fulcrum load
3rd Class Levers— • The input force (effort) is between the • fulcrum and the load • Do not change the direction of the input force • Does not multiply your input force (effort) but allows you to apply a lot of force over a shorter distance • Examples: Tweezers, Rake, baseball bat, Hammer
Remember FLE 1st Class– fulcrum in the middle 2nd Class– load is in the middle 3rd Class– Effort (input force) is in the middle load Input force (effort) fulcrum Output/load effort fulcrum