Forces, Waves and Electricity 26%

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

Acceleration Acceleration = rate at which velocity changes Involves a change in speed OR direction a = (vf – vi )/ t Units of acceleration = m/s2 Example: 0 to 60 mph in 5 seconds For acceleration to occur a net (unbalanced) force must be applied

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 = -0.25 m/s2

Newton’s 1st 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 2nd Law of Motion Force = mass x acceleration F = ma

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

Mass- stays the same Weight- changes gravity decreases, weight decreases Mass is in g, kg Weight is is Newtons

Falling objects and gravity Force, mass, and acceleration are interdependent.  A change in any one of these affects the others. Friction is an ever present force that opposes motion. All objects fall at the same speed independent of its mass if there are not frictional forces acting upon them.

Falling objects and gravity An astronaut on the moon drops a feather and a rock from the same height. They reach the ground at the same time. Why does this happen on the moon but NOT on Earth? The moon has no atmosphere. The moon’s weaker gravity pulls each with less force. Objects dropped on Earth are not influenced by lunar gravity. On Earth, the rock has more mass due to Earth’s stronger gravity

where force and distance are in same direction 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(J)

Static Equilibrium If the combined effect of all the forces acting on a body is zero and the body is in the state of rest then its equilibrium is termed as static equilibrium.    

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

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

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

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

A scientist investigates the type of radiation being emitted by a radioactive sample. An apparatus is constructed using a radiation detector, a radioactive sample, and two different types of absorbers placed between the detector and the sample. Absorber used Average counts per second No absorber 33 Paper 1 mm thick 20 Metal 3 mm thick 1

Question Which type(s) of radiation does the sample emit? A. The sample emits alpha radiation. B. The sample emits beta radiation. C.*The sample emits both alpha and beta radiation. D. The sample emits neither alpha nor beta radiation.

vacuum of space Light but NO sound

Speed of Sound empty space gas none slowest liquid solid fastest

Light faster than Sound Thunder & lightning L then T thunder and lightning L then T Light faster than Sound Thunder & lightning L then T Light faster than sound Thunder

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

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

This diagram shows two overlapping waves with the same wavelength and amplitude. Which statement correctly explains the diagram? A. The waves overlap and increase in frequency. B. The wave frequencies overlap and increase refraction. C. Diffraction between the waves increases the amplitude. D. Interference between the waves increases the amplitude.

Which diagram represents interference?

incoming departing Increase frequency, Decrease frequency Doppler Effect Increase frequency, Decrease frequency incoming departing

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

Ohm’s Law and electricity In a direct current (DC) circuit, the relationship between the current (I) passing through a resistor, the potential difference (V) across the resistor, and the resistance (R ) of the resistor is described by Ohm’s Law: V = IR.   Find this formula On your Formula Sheet

Direct Circuits (DC) The "I" is thought to have been meant to represent "Intensity" (of electron flow) Free electrons tend to move through conductors with some degree of friction, or opposition to motion. This opposition to motion is more properly called resistance The force motivating electrons to "flow" in a circuit is called voltage. Voltage is a specific measure of potential energy that is always relative between two points

What is the amount of voltage provided by the battery? V= IR V= (2A) X 7 V=14

Practice What formula do you use? How many volts is in this circuit? How many Ohms? How much current?

Electrical Circuits Current flows in a closed circuit Ohm’s Law V = IR Two types of circuits: Series (single path)-Christmas tree lights Parallel (many paths)-houses SERIES PARALLEL

Permanent Magnets

ELECTROMAGNET Stronger: more loops stronger battery

“Mag”nificent Information Even the most powerful permanent magnet is not as strong as the stronger electromagnets, so their applications are limited, but they still have many uses. Magnets can be found everywhere, including your computer, ATM and credit cards, speakers and microphones, electric motors, and toys. Electric motors work through an interaction between an electromagnet and a permanent magnet .

Waves – Electricity Hertz – frequency Volts- Potential Difference Voltage V Amps- Current A Ohms- Resistance Ω

1.WRITE DOWN WHAT YOU KNOW BEFORE YOU START!!!! Remember to…. 1.WRITE DOWN WHAT YOU KNOW BEFORE YOU START!!!! 2.Take your time 3.Guess if you need to