Forces, Waves, and Electricity Georgia High School Graduation Test: Science Review Mrs. Kirby

Introduction From the key vocabulary, circle the words that you can already define or use in a sentence. Write down two or three things that you think are important for you to know today.

Speed and Velocity Speed = distance divided by time s = d/t Units of speed = m/s Velocity = speed in a given direction Example:  55 mph = speed  55 mph north = velocity

Distance versus Time Graph AKA position versus time graph Straight line represents constant (uniform) speed

Acceleration Acceleration = rate at which velocity changes Involves a change in speed OR direction a = (v f – v i )/ t Units of acceleration = m/s 2 Example: 0 to 60 mph in 5 seconds For acceleration to occur a net (unbalanced) force must be applied

Distance versus Time Graph Revisited Non-linear graph represents acceleration Parabola = constant acceleration

Sample Question #1 Use the equations for velocity and acceleration to solve the following examples:  A ball rolls in a straight line very slowly across the floor traveling 1.0 meter in 2.0 seconds. Calculate the velocity of the ball. Answer: v = 0.50 m/s  If the ball from the above question rolls to a stop in 2.0 seconds, calculate the acceleration (deceleration) of the ball. Answer: a = m/s 2

Forces Force = a push or a pull Net Force = sum of all forces acting on an object Free-body diagram shows all forces with vector arrows Direction of force = direction of acceleration Friction is a force that always opposes motion

Determining the Net Force

Newton’s 1 st Law of Motion  An object at rest will remain at rest and an object in constant motion will remain in constant motion unless acted on by an unbalanced force.  Reason for seatbelts

Newton’s 2 nd Law of Motion Force = mass x acceleration F = ma

Newton’s 3 rd Law of Motion For every action, there is an equal but opposite reaction Examples:  Punch a wall, it punches back  Rocket propulsion

Gravity Gravity = attractive force between two objects that have mass Makes falling objects accelerate (g = 9.8 m/s 2 ) Depends on mass and distance

Sample Question #2 What causes an object to accelerate as it falls?  Answer: The force of gravity causes an object to accelerate at a rate of 9.8 m/s 2 toward Earth.

Mass versus Weight MASS measure of the amount of matter in an object measured in kilograms does not depend on location  an object’s mass on Earth is the same as its mass on the Moon WEIGHT measure of the force of gravity on an object measured in Newtons does depend on location  an object’s weight on Earth is more than its weight on the Moon

Sample Question #3 Explain the difference between mass and weight.  Answer: Mass is the quantity of matter of an object while weight is the measure of the force of gravity on that object. Mass is conserved while weight may change depending on location.

Energy and Work Energy = The ability to do work Work = transfer of energy by applying a force to move an object W = Fd where force and distance are in same direction Both work and energy are measured in Joules

Examples of Work and No Work Hammer applies a force to move the nail in the same direction = WORK Waiter applies a force upward while the tray moves forward = NO WORK

Sample Question #4 Use the formula for work to solve the following example:  A woman picks up her 10 Newton child lifting him 1 meter. She then carries him 5 meters across the room. How much work is done on the child? Answer: 10 Joules the 5 meters is not added to the 1 meter because the distance moved (5 meters) is perpendicular to the force applied

Types of Mechanical Energy Kinetic = energy of motion Potential = stored energy due to position

Conservation of Energy

Light Light is a form of electromagnetic radiation (EM) EM spectrum shows the forms of radiation in order of increasing frequency (and energy) and decreasing wavelength

Color of Light We see different colors depending on the frequency of light emitted or reflected This is the reason blue flames are hotter than yellow. Blue has a higher frequency so more energy.

Sample Question #5 How are the frequency and wavelength related to the energy carried by waves?  Answer: Higher frequency waves have more energy while longer wavelength waves have less energy. Frequency and energy are directly related while wavelength and energy are inversely related. Radio waves (long wavelength) have less energy than gamma waves (high frequency).

Sample Question #6 How are frequency and wavelength related?  Answer: Frequency and wavelength are inversely related. High frequency waves have short wavelengths.

Electromagnetic Wave (EM) versus Mechanical Wave EM WAVE does not require matter to transfer energy CAN travel through a vacuum example: light MECHANICAL WAVE does require matter to transfer energy CANNOT travel through a vacuum example: sound

Sample Question #7 Compare electromagnetic and mechanical waves.  Answer: Electromagnetic waves (light) do not require matter to transfer energy while mechanical waves (sound) require matter to transfer energy. In other words, EM waves will travel in a vacuum while mechanical waves will not.

Reflection of Light When light strikes a boundary, it reflects. The angle at which the wave approaches a flat reflecting surface is equal to the angle at which the wave leaves the surface (like a bounce pass of a basketball). Reflection results in image formation.

Refraction of Light Light waves travel faster in air than in water and slower in glass than water. More dense = slower light When light enters a different medium, speed changes and it bends. Bending of light due to change in speed = REFRACTION

Wave Interference the phenomenon which occurs when two waves meet while traveling along the same medium constructive = waves add to produce a larger wave destructive = waves cancel to produce a smaller wave CONSTRUCTIVE DESTRUCTIVE

The Doppler Effect observed whenever the source of waves is moving with respect to an observer an apparent change in frequency occurs toward = higher frequency away = lower frequency

Electricity Electrons carry a negative charge. Lost electrons = positive charge Gained electrons = negative charge REMEMBER:  Like charges repel  Opposites attract

Electrical Circuits Current flows in a closed circuit Ohm’s Law  V = IR Two types of circuits:  Series (single path)  Parallel (poly paths) SERIES PARALLEL

Electromagnet One can make an electromagnet with a nail, battery, and wire When current flows through the coiled wire, the nail becomes magnetized.

Discussion Aristotle claimed that objects fell at a rate proportional to their weight, so that heavier objects fell faster than lighter objects. Explain why you think he was correct or he was wrong. How could one determine whether or not he was correct?

Lesson Summarized Write a sentence that explains the system being discussed. Draw a graphic organizer for each system in this lesson. Show the relationship of the parts of the system to the whole within each system.

Short Quiz Answers 1.A force is a push or a pull. Unbalanced (net) forces result in acceleration. 2.The object ejected from a spacecraft near Earth will most likely fall into the Earth due to gravity while the object ejected in deep space will travel at a constant speed until acted on by an unbalanced force (Newton's First Law of Motion). 3.Sound and ocean waves are both mechanical waves because they both require matter to transmit energy. 4.Light and sound both transfer energy, but light does not require matter to transfer energy while sound does. In other words, light waves will travel in a vacuum while sound waves will not.