Chapter 5 Matter in Motion Focus Notes

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Lucas Maurice Greene
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1 Chapter 5 Matter in Motion Focus Notes

2 Section 1 Define the following terms: Motion, Speed, Velocity, and Acceleration Motion: an object s change in position relative to a reference point. Speed: the distance traveled divided by the time interval during which the motion occurred (S=D/T). For example: 25 mph (miles per hour) or 10 m/s (meters per second) Velocity: the speed of an object in a particular direction. For example: 25 mph NORTH or 10 m/s SOUTH Acceleration: The rate at which velocity changes over time; an object accelerates if its speed, direction, or both change.

3 Section 1 What is a reference point? An object that appears to stay in place in relation to motion. Describe the motion of an object by position of the object in relation to a reference point. If you are riding in a car, how do you know you are moving? What stays still while you move? Trees, Buildings, etc. Identify the 2 factors that determine speed. Distance and Time What is the SI unit for speed? Meters per second (written m/s); Can also be km/h

4 Section 1 What formula do you use to calculate average speed? Average Speed = TOTAL distance/ TOTAL time. Calculate the average speed in the 3 questions below: Kira jogs to a store 72 m away in a time of 36 s. What is Kira s average speed? 72/36 = 2 m/s If you travel 7.5 km and walk for 1.5 h, what is your average speed? 7.5/1.5 = 5 km/h An airplane traveling from San Francisco to Chicago travels 1,260 km in 3.5 h. What is the airplane s average speed? 1,260/3.5 = 360 km/h

5 Section 1 What are the 2 ways velocity can change? When speed or direction change. What is resultant velocity? How is it calculated if velocities are moving in the same direction? In opposite directions? Resultant velocities occur when velocities are combined. Velocities in the SAME direction are ADDED together. With Velocities traveling in OPPOSITE directions you TAKE THE DIFFERENCE and keep the directionality of the HIGHER velocity! Explain the difference between speed and velocity. Speed is calculated by dividing DISTANCE by TIME; Velocity IS speed, but with a DIRECTION on the end.

6 Section 1 What is an increase in velocity typically called? How about a decrease in velocity? Increase in velocity is called POSITIVE acceleration. Decrease in velocity is called NEGATIVE acceleration (or deceleration). Complete the statement: The faster the velocity changes, the greater the ACCELERATION is. Analyze the relationship between velocity and acceleration. As an objects VELOCITY changes (either by changing direction or speed) an object ACCELERATES! VELOCITY CAUSES ACCELERATION!

7 Section 1 What is the formula for calculating average acceleration? Average Acceleration = Final Velocity-Starting Velocity/Time it takes to change velocity. What is the average acceleration of a subway train that speeds up from 9.6 m/s to 12 m/s in 0.8 s on a straight section of track? 12 m/s 9.6 m/s / 0.8 s = 3 m/s 2 (Since Velocity is expressed in m/s and Time is expressed in seconds, the Acceleration unit is m/s 2 or meters per second per second!) Why is it more helpful to know a tornado s velocity rather than its speed? Velocity includes direction. In the case of a tornado, you need to know the speed, but the direction is more important so people can evacuate out of the path.

8 Section 1 Draw a graph showing speed. Draw a graph showing acceleration.

9 Section 1 Explain centripetal acceleration. Acceleration in a circular motion; it is CONSTANTLY accelerating WHY?? It is CONSTANTLY changing direction!

10 Section 2 Define the following terms: Force, Newton, and Net Force Force: any push or pull exerted on an object in order to change the motion of the object; it has size and direction Newton: the SI unit for force, symbol N Net Force: the combination of all of the forces acting on an object. What unit is used to express force? Newton 1 Newton = 100 grams?

11 Section 2 Describe forces, and explain how forces act on objects. Forces act on ALL objects! For any push to occur, something has to receive the push. You can t push nothing! However, not all forces cause motion to occur (gravity). How do you calculate Net Force when forces are acting in the same direction? In opposite directions? Net forces acting in the SAME direction are ADDED together. While Net Forces acting in OPPOSITE directions - take the difference and keep the DIRECTION of the HIGHER force (just like Resultant Velocities).

12 Section 2 Create a table comparing the characteristics of balanced and unbalanced forces. Balanced Forces Net Force = ZERO Newtons Does not cause a change in motion to a moving object Does not cause a nonmoving object to start moving. Unbalanced Forces Net Force does NOT = ZERO Newtons Cause a change in motion, like speed or direction cause acceleration! Necessary for an object to change motion or move.

Section 2 The force of your desk pushing up on your book is balanced by what other force pushing down? GRAVITY! Describe 2 ways that unbalanced forces cause changes in motion.

13 Section 2 The force of your desk pushing up on your book is balanced by what other force pushing down? GRAVITY! Describe 2 ways that unbalanced forces cause changes in motion. Causing the direction or speed to change causing Acceleration to occur! A boy pulls a wagon with a force of 6 N east as another boy pushes it with a force of 4 N east. What is the net force? 6 N east + 4 N east = 10 N east

14 Section 3 Define the following term: Friction Friction: A force that opposes motion between 2 surfaces that are in contact. Explain why friction occurs. Friction occurs because the surface of any object is rough.

15 Section 3 Draw a picture showing friction between 2 objects.

16 Section 3 Why is friction greater between surfaces that are rough? Rough surfaces have more microscopic hills and valleys. What is the relationship between force and friction? The greater the force, the greater the friction. What are the 2 types of friction? Kinetic and Static Friction

17 Section 3 Sliding Friction Rolling Friction

18 Section 3 Explain how static friction works on a book sitting on a table. There is no friction between the book and table when no force is being applied. When a small force is applied, the book doesn t move because it has not overcome the frictional force. When a large force is applied, the book moves since the force applied has overcome the frictional force. List 2 ways that friction can be helpful. Brakes on a car; Allows you to write on your paper! List 2 ways that friction can be harmful. Engine parts experiencing friction will ruin your car; Friction by wind or water causes erosion.

19 Section 3 How can friction be reduced? By adding a lubricant; changing from sliding to rolling friction. How can friction be increased? Make surfaces rougher (sand paper); increase the force applied.

20 Section 4 Define the following terms: Gravity, Weight, and Mass Gravity: a force of attraction between objects that is due to their masses Weight: measure of gravitational force exerted on an object; varies by location (unit is Newton) Mass: amount of matter in an object (unit is Gram/Kilogram); does NOT change based on location

21 Section 4 Describe gravity and its effects on matter. All matter has mass. Gravity is a result of mass. So, all matter is affected by gravity. ALL objects have a gravitational attraction to each other YES, ALL OBJECTS! We don t notice this attraction because it is so small that it appears insignificant. Why must you exert a force to pick up an object? What must you overcome? You must overcome GRAVITY to lift any object. Who is known as the father of gravity? What is the story as to how gravity was discovered? Isaac Newton. The Falling Apple story Newton sat under a tree and saw an apple fall and thought there had to be forces at work he called the force gravity.

22 Section 4 What are the 2 parts of the Universal Law of Gravitation? Part 1: Gravitational force Increases as MASS Increases. Part 2: Gravitational force Decreases as DISTANCE Increases. Why is the Universal Law of Gravitation universal? It is valid EVERYWHERE in the UNIVERSE!

23 Section 4 Draw a picture explaining the 2 parts of the Universal Law of Gravitation. DISTANCE MASS

24 Section 4 How does mass effect gravitational force? Larger mass = Larger Gravitational force; Smaller mass = Smaller Gravitational force Create a table comparing weight and mass. Weight Mass Changes based on location Always stays the same Measured in Newtons Measured in Grams

25 Section 4 How does the mass of an object relate to the gravitational force that the object exerts on other objects? The larger the mass, the larger the force and vice versa. The gravitational force on Jupiter is approximately 2.3 times the gravitational force on Earth. If an object has a mass of 70 kg and a weight of 686 N on Earth, what would the object s mass and weight on Jupiter be? Mass = 70 kg (stays the same) ; Weight = 2.3 X 686 N = N How do you explain to someone who has no knowledge of gravity that gravity exists in space? Gravity holds the planets in orbit around the sun. Why does your weight change if you landed on Mars, but your mass does not? Weight is a measure of gravitational force, while mass is constant.

26 Wrapping Up Explain why it is important for airplane pilots to know wind velocity and not just wind speed during a flight. Pilots need to know the directionality of the wind as well to be able to adjust during a flight. How is it possible to be accelerating and traveling at a constant speed? A change in direction (change in velocity) causes acceleration.

27 Wrapping Up You observe the effects of gravity every day. What 2 quantities does gravitational force depend on? How do those quantities affect the size of the gravitational force between 2 objects? Gravitational Force depends on the mass of objects and the distance between the objects. Gravitational force increases as the mass of one or both of the objects increases. Gravitational force decreases as the distance between the objects increases.

Wrapping Up A downhill skier has her skis sharpened and waxed before every race. What effect would this have on her performance? Reduces the friction.

28 Wrapping Up A downhill skier has her skis sharpened and waxed before every race. What effect would this have on her performance? Reduces the friction. How will the motion of a ball rolling on the ground change if the ball encounters a frictional force that opposes its motion? The ball will slow down.

2. What is the force weight of a 45 kg desk? 3. Give a scenario example for each of Newton s Laws.

Catalyst 1.What is the unit for force? Newton (N) 2. What is the force weight of a 45 kg desk? 3. Give a scenario example for each of Newton s Laws. HANDS UP!! 441 N 4. What is net force? Give an example.