# Electricity and Magnetism

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Electricity and Magnetism
PHYSICS Units: Analyzing Motion Work and Energy Waves Electricity and Magnetism

TN Standards - Motion CLE : Investigate the relationships among speed, position, time, velocity, and acceleration CLE.3202.Inq.2: Design and conduct scientific investigations to explore new phenomena, verify, previous results, test how well a theory predicts, and compare opposing theories CLE.3202.Inq.4: Apply qualitative and quantitative measures to analyze data and draw conclusions that are free of bias CLE.3202.Inq.6: Communicate and defend scientific findings

Chapter 11 - Motion Sections: 1 - Measuring Motion 2 - Acceleration
3 - Motion and Force

1 - Measuring Motion Key Questions:
How is a frame of reference used to describe motion? What is the difference between speed and velocity? What do you need to know to find the speed of an object? How can you study speed by using graphs?

Frame of Reference Observe an object in relation to other objects that stay in place, called reference points. A frame of reference is used to describe the motion of an object relative to these reference points. The trees in the background in Figure 1

Distance Distance measures the path taken
To measure distance, you measure the length of the path that the object took. Displacement measures only the difference between the final and starting positions

Speed & Velocity Speed – how fast an object moved
Velocity – gives us both speed and direction Velocity is described relative to a reference point Up and right are positive; left and down are negative ( Cartesian Coordinate system ) +y -x +x -y

Motion When an object changes position with respect to a frame of reference, the object is in motion Velocity / Speed: Distance travelled in a certain time period D V/S t

D V/S t Calculating Speed
Need two quantities – distance travelled & time Average speed – distance divided by time interval Instantaneous speed speed at a given time very small time interval Speedometer in car D V/S t

Demonstration Slope of a distance vs. time graph equals speed
Run a 6 m length ( in class? ) Have your partner time you What is your speed?

Graphing Motion Sometimes easier to analyze motion on graphs

2 - Acceleration Key Questions:
What changes when an object accelerates? How do you calculate the acceleration of an object moving in a straight line? How can a graph be used to find acceleration?

Velocity Changes upon Acceleration
Speed can change, but so can direction Notice speed is changing with each second

Changes in Direction Uniform circular motion has centripetal acceleration Sources: friction, tension Demonstration

Circular Motion Demonstration
Foam ball with string attached to it Swing ball with hand Diagram features of motion What happens when I let go of the string?

2 - Acceleration Key Questions:
What changes when an object accelerates? How do you calculate the acceleration of an object moving in a straight line? How can a graph be used to find acceleration?

BELLWORK What changes when acceleration occurs?

2 - Acceleration Key Questions:
What changes when an object accelerates? How do you calculate the acceleration of an object moving in a straight line? How can a graph be used to find acceleration?

Calculating Acceleration
V A t

Calculating Acceleration
Acceleration is the rate at which velocity changes Acceleration is negative when slowing down

Graphing Accelerated Motion
The slope of a straight line on a speed vs. time graph is equal to the acceleration. Constant Acceleration Can also be seen from a distance vs. time graph

BELLWORK How do we calculate average acceleration?

3 - Motion and Forces Key Questions:
What do scientists identify as the fundamental forces of nature? What happens when there is a net force acting on an object? What force always opposes motion? Why is friction sometimes necessary?

Fundamental Forces A Force is defined as any action that can change the state of motion of an object Gravity, electromagnetic force, strong nuclear force, and the weak nuclear force Fundamental forces vary in strength Forces can act through contact or at a distance

Balanced and Unbalanced Forces
Whenever there is a net force acting on an object, the object accelerates in direction of the net force Balanced forces do not change motion Unbalanced forces do not cancel each other

Friction Is a force Always opposes motion
Static friction – occurs between stationary surfaces Kinetic friction – occurs between moving surfaces Sliding friction ( usually greater than rolling fiction ) Rolling friction

Friction and Motion Friction is necessary for many everyday tasks to function properly Non-stick skillets Cars would not move without friction!! Can increase helpful friction or decrease unwanted friction Sand on roads make them less slippery Lubrication reduces friction

Friction and Balance of Forces
Cars do not or do move based on friction Constant speed Acceleration No Slipping

Demonstration – Spring Scale
Drag wood and measure the force needed to overcome friction Friction depends on force applied between surfaces Rock keeps paper from being blown away by wind More weight on block  more friction Rougher surface  more friction