Energy

1. Energy

2. Energy Law of conservation of energy • Energy can neither be created nor destroyed. • It can be changed into other forms.

3. Two Kinds of Energy Potential energy is stored energy or energy of position. • Examples: Magnetic, gravitational, chemical, elastic, and nuclear PE = mgh where m= mass g= acceleration due to gravity h= height Kinetic energy is energy of motion or energy in action. • Examples: a moving baseball or a roller coaster going downhill KE = ½ mv2

4. Forms of Energy Mechanical Energy- any object which possesses mechanical energy - whether it be in the form of potential energy or kinetic energy - is able to do work. That is, its mechanical energy enables that object to apply a force to another object in order to cause it to be displaced

5. Mechanical Energy Simple machines help us lift, pull, increase elevation of heavy things, change the direction of the force, increase the force, split things, fasten things, and cut things • Inclined plane - Ramp, stairs • Wedge – two inclined planes back to back – screwdriver, knife, axe • Screw – inclined plane wrapped around a cylinder • Pulley – rope revolves around a fixed point; more pulleys make work easier • Lever – has a fulcrum – see-saw • Wheel and axle – bicycle, car, doorknob, screwdriver in use

6. Simple Machines

7. Mechanical Advantage Mechanical advantage-the number of times a machine multiplies an effort force. Formulas from formula sheet Actual Mechanical Advantage: where FR is Force due to resistance and FE is Force due to effort OR IMA: Effort Length Resistance Length

8. Heat, Temperature, and Internal Energy • The temperature of an object is directly proportional to the average kinetic energy of its particles. As temperature goes up, particles move faster. • The Internal Energy of a substance is total of the potential and kinetic energy of all its particles. • Energy moving from one location to another is known as heat. Objects do not contain heat. Instead they contain internal energy

9. Chemical Energy Chemical energy relates to potential energy stored in the bonds between atoms in a compound

10. Wave Energy Basic Wave Vocabulary: • Amplitude – the height of a wave as measured from its equilibrium position • Frequency – the number of wave cycles per unit time • Hertz – common unit for frequency, means the same as cycles per second • Wavelength – the distance between two identical points on adjacent waves. It is often measured “crest to crest.” • Period – the time required to complete one cycle

11. Wave Energy

12. Types of Waves A wave is a disturbance of a medium which transports energy through the medium without permanently transporting matter. In a wave, particles of the medium are temporarily displaced and then return to their original position.

13. Transverse Wave Waves in which the particles of the medium move in a direction that is perpendicular to the direction of the wave are known as transverse waves. Transverse waves require a relatively rigid medium in order to transmit their energy. • Examples of transverse waves include waves on a string

14. Longitudinal Wave A longitudinal wave is a wave in which particles of the medium move in a direction parallel to the direction which the wave moves. • Examples of longitudinal waves include sound waves.

15. Surface Wave A surface wave is a wave in which particles of the medium undergo a circular motion. Surface waves are both longitudinal and transverse. • Seismic(earthquake) and water waves are examples of surface waves.

16. Light- Electromagnetic Spectrum • Colors of visible light- ROYGBIV which is red, orange, yellow, green, blue, indigo, violet • All electromagnetic waves travel at the speed of light 3.0 x 108 m/s in a vacuum.

17. Reflection Reflection occurs when a wave encounters a new medium and bounces off of it. • The Law of Reflection states that the angle of incidence (the angle between the incoming wave and the normal) must equal the angle of reflection (the angle between the reflected wave and the normal). The normal is a line perpendicular to the surface.

18. Refraction Refraction occurs when a wave travels at an angle from one medium to another in which its speed is different. The difference in speed causes the wave to bend. Refraction is why objects in a pool are difficult to locate when viewed from above and why a pencil looks broken when part of it is placed in a glass of water.

19. Diffraction Diffraction involves the bending of waves around obstacles. Diffraction can occur with any kind of wave. Diffraction explains why sound can be heard around corners.

20. Interference Constructive interference occurs when two waves disturb the medium in the same way. The disturbance is larger than the disturbance of either wave separately. Destructive interference is canceling interference that occurs when two waves disturb the medium in opposite ways. The disturbance is smaller than the disturbance of either wave separately.

21. Interference

22. Sound Sound waves are mechanical waves, meaning they must have a medium to travel through. (There is no sound in space.) A sound wave is a compressional or longitudinal wave. This means the particles of the medium move in the same direction as the wave. Sound travels fastest in solids, second fastest in liquids, and slowest in gases. As the temperature increases, the speed of sound also increases. Different sounds appear different because they have different pitch or frequency.

23. Gravitational Forces The force of gravity between any two objects increases as the mass of either object increases. The force of gravity decreases as the distance between the objects increases. The force of gravity experienced by something is also known as its weight. Weight can be calculated multiplying mass by the acceleration of gravity (g). W=mg Weight depends on both mass and the acceleration of gravity. Mass depends only on the amount of matter in an object. Mass does not change when the location of an object changes. The force and weight are both measured in Newtons. Mass is measured in kilograms. Acceleration is measured in m/s/s (m/s2).

24. Gravitational Forces Free Fall: a free-falling object is an object which is falling under the sole influence of gravity. • Free-falling objects do not encounter air resistance. • All free-falling objects (on Earth) accelerate downwards at a rate of approximately 10 m/s/s (to be more exact, 9.8 m/s/s). This quantity known as the acceleration of gravity has a special symbol to denote it - the symbol g. The distance traveled by a falling object is calculated using the formula, d = ½ gt2

25. Electromagnetic Forces Electromagnetic Forces – like charges repel each other, opposite charges attract. • As the distance between the charges increase, the magnitude of the force decreases. The same holds true for magnets. • Magnets will always have a North Pole and a South Pole. Just like with electrical charges, opposite poles attract. While it is possible to separate positive and negative charges, it is impossible to separate north and south magnetic poles.

26. Electromagnetic Forces Electric and Magnetic Field Lines- The lines always go from positive charges to negative charges and from north poles to south poles. The closer the lines, the stronger the field. Magnetic field is strongest where the lines are closer together

27. Electromagnet • List a use for electromagnets. • Lift and move cars in a junk yard • 2. How can you make a stronger • electromagnet? • a. More coils of wire around the nail • b. More batteries

28. Work Work- two conditions must be met for work to occur • the object must move through a distance • a force must act upon the object in the direction the object moves • SI unit for work is the joule, J. (Newton-meter) • Formula: work = force X distance W=F X d • When an object is lifted to a new location or pushed up a ramp, the work equals the potential energy gained. Sample Problem: What work is done if Hernando uses 88 N of force to pull a table 12 meters? F = 88N Use the formula W=F X d d = 12 m from the W=88N X 12 m SCIENCE FACTS & FORMULAS sheet W= 1056 N-m or 1056 J

29. Power Power- the rate of work • SI unit is the watt, W (joule/second) • Formula: power = work/time (work divided by time) Sample Problem: When doing a chin-up, a physics student lifts her 40-kg body [which has a force (weight) of 400 N] a distance of 0.25 meters in 2 seconds. What is the power delivered by the student's biceps? You must first calculate the work done to lift her body W = F X d = (400 N) (0.25 m) W = 100 J To calculate power: Power= work Power= 100 J time 2 sec Power = 50 Watts

30. Newton’s Laws of Motion The Law of Inertia or Newton’s First Law: An object at rest tends to stay at rest and an object in motion tends to remain in motion in a straight-line path unless acted on by an unbalanced force. • Inertia is another word for mass. The more mass an object has, the greater its tendency to maintain its current state.

31. The Law of Inertia or Newton’s First Law Applications • People are often thrown from automobiles in wrecks because the car comes to a sudden stop, but the person has a tendency to stay in motion. • The ride is much smoother on a cruise ship than a fishing boat, because the cruise ship is more massive and is not affected as much by the waves.

32. Newton’s Second Law Newton’s Second Law- the acceleration of an object is directly proportional to the applied force and inversely proportional to its mass. F=ma F= force m = mass a = acceleration • Sample Problem: What is the force exerted by a 2 kg mass that accelerates at 3 m/sec/sec? mass=2 kg F=ma acceleration=3 m/sec/sec F =2 kg x 3 m/sec/sec F=6 kilogrammeter/sec/sec Check the SCIENCE FACTS AND FORMULAS sheet 1 newton = 1 kilogrammeter/second/second Correct answer is 6 newtons.

33. Newton’s Third Law Newton’s Third Law- for every action there is an equal and opposite reaction. • If object A exerts a force on object B, then object B exerts an equal force on object A in the opposite direction. • Consequences: Forces always exist in pairs. It is impossible for you to push on something without it pushing back. Newton’s Third law can be used to explain the motion of rockets and balloons. As the gases exit the balloon or rocket, they push it in the opposite direction.

34. Newton’s Laws of Motion Motion depends on the observer’s frame of reference

35. Speed Speed- a measure of how fast something is moving; the distance traveled in a given amount of time • Formula speed = distance time Sample Problem: A bicyclist rides for 1.5 hours from Snellville to downtown Atlanta. He travels 21 miles. What is his average speed? d=21 miles Speed= distance t=1.5 hours time Speed= 21 miles 1.5 hours Speed = 14 mi/hr

36. Velocity Velocity- speed in a particular direction • Formula: velocity = distance and direction Time The formula from the SCIENCE FACTS AND FORMULAS sheet is Velocity (V) = V0 + at, where V0 = Initial Velocity, a = Acceleration, and t = Time Sample Problem: What is the average velocity of a commercial jet that travels west from New York to Los Angeles (4800 km) in 6.00 hours? Velocity = distance time = 4800 km 6.00 hours = 800 km/hr west

37. Acceleration Acceleration- the rate at which velocity changes • Formula: acceleration = final velocity-initial velocity time or acceleration = from SCIENCE FACTS AND FORMULAS sheet Acceleration = Change in Velocity/Time Elapsed Acceleration occurs if either of these two conditions exist: • The speed of an object is changing. It can be increasing or decreasing • The direction of the movement is changing.

38. Acceleration Sample Problem: If a car accelerates from 5 m/s to 15 m/s in 2 seconds, what is the car's average acceleration? V = 15 m/s Vo = 5 m/s a= 15 m/s - 5 m/s t = 2 sec 2 sec a= 5 m/sec/sec

39. Questions?