Review Video: Motion in a straight line

1. Review Video: Motion in a straight line https://www.youtube.com/watch?v=ZM8ECpBuQYE

2. Acceleration

3. Velocity – includes speed of an object and the direction of its motion Essential Question: What is the difference between speed & velocity? Velocity includes direction where as speed does not.

4. I. What is Acceleration? A. The speed of things is always changing. For example, your car speeds up and slows down in stop and go traffic. Slowing down gradually in your car feels very different from slamming on the brakes and stopping fast. B. The rate at which the speed of something changes is called it’s acceleration.

5. I. What is Acceleration? C. Acceleration is the rate of change in the speed of an object. Rate of change means the ratio of the amount of change divided by how much time it took to change. D. In other words, acceleration is how much your speed changes over time.

6. Acceleration – rate of chance of velocity. Acceleration occurs when an object changes speed, its direction, or both.

7. Calculating Acceleration Acceleration (meters/second²) = change in velocity (meters/sec) Time (seconds) * NOTE : Change in velocity = final velocity – initial velocity V = Vf - Vi Acceleration formula : a = Vf – Vi t

8. Positive Acceleration A plane takes off… a = Vf – Vi = 80m/s – Om/s t 20s a = 4m/s² The plane is speeding up so acceleration is positive.

9. Negative Acceleration A bike comes to a stop… a = Vf – Vi = 0m/s – 3m/s t 2s a = -1.5m/s2 The bike is slowing down so acceleration is negative.

10. II. Acceleration Example • Suppose you are driving and your speed goes from 20 mph to 60 mph in four seconds. • The amount of change is 60 mph minus 20 mph, or 40 mph. • The time it takes to change is 4 seconds. • The acceleration is 40 mph divided by 4 seconds, or 10mph/s. • This means that your speed increased by 10 mph every second.

11. II. Acceleration Example The table below shows your speed while accelerating

12. III. Calculating Acceleration A. Acceleration is the change in speed divided by the change in time B. The formula is Acceleration = Change in Speed Change in Time

13. III. Calculating Acceleration Acceleration Problem Solving Steps • Make sure you have 2 speeds and 2 times (remember that acceleration is change in speed divided by change in time) • Calculate the change in speed by subtracting the final speed - the initial speed • Calculate the change in time by subtracting the final time - the initial time

14. III. Calculating Acceleration 4. Divide the change in speed by the change in time

15. III. Calculating Acceleration D. Acceleration Problem: If a car is traveling at 30 miles per hour and speeds up to 60 miles per hour in 6 seconds, what is the acceleration? 1. Speeds 30 mph to 60 mph, time difference is 6 seconds 2. Change in speed: 60 mph - 30 mph = 30 mph 3. Change in time: 6 seconds

16. III. Calculating Acceleration 4. Change in speed Change in time 30 mph = 5 mph/s 6 seconds So each second, the speed increases 5 mph

17. IV. Units of Acceleration C. What this means is that the acceleration is the amount that the speed changes in each second. D. The common unit for acceleration is m/s2 – meters per second squared

18. V. Different Accelerations • Acceleration means ANY change in speed or velocity. • There can be negative acceleration or zero acceleration. • If you are slowing down, then you have a negative acceleration.

19. V. Different Accelerations D. If your speed is not changing, then you have zero acceleration. For example, if you are traveling on a highway with cruise control, then you have zero acceleration.

20. Warm Up How do you use forces every day? Think about how it applies to a volleyball or football game. Write 5 examples of Forces you experience every day.

21. FORCE • A push or pull • Required for anything w/ mass to accelerate • 1N = 1kg x 1m/s2 • Double the mass :: Double the force • 2N = 2kg x 1m/s2 • Double the speed :: Double the force • 2N = 1kg x 2m/s2 • Double mass and speed :: 4x the force • 4N = 2kg x 2m/s2

22. Net Force – When two or more forces act on an object at the same time FORCES UNBALANCED NET FORCE = + FORCES ARE = BALANCED FORCES NET FORCE = 0 COMBINED FORCES NET FORCE = TWO FORCES ADDED TOGETHER

23. Newton’s First Law of Motion Also known as Law of Inertia! An object in motion stays in motion, or an object at rest stays at rest until an unbalanced net force acts upon it.

24. I. Newton’s 1st Law • Inertia is defined as the property of an object to resist changing it’s state of motion. • Newton’s 1st law is also called the law of inertia. • Newton’s first law states that an object at rest will remain at rest unless acted on by a force, and an object in motion will stay moving unless acted on by a force.

25. 5.5min Video: Newton’s 1st Law https://www.youtube.com/watch?v=LEHR8YQNm_Q

26. Inertia – tendency of an object to resist any change in its motion. WILL STAY AT REST UNTIL FORCE ACTS IN IT WILL CONTINUE IN MOTION UNTIL THESE FORCES ACT ON IT GRAVITY FRICTION WALL

27. I. Newton’s 1st Law D. In simpler terms, this means that unless you apply a force, things tend to keep on doing what they were doing in the first place.

28. Newton’s Second Law of Motion A net force acting on an object causes the object to accelerate in the direction of the force. Acceleration is determined by size of force and the mass of an object. (Kg * m/s²) (kg) (m/s²) Force = mass x acceleration F = m x a

29. 5min Video: Newton’s 2nd Law https://www.youtube.com/watch?v=ZvPrn3aBQG8

30. 4.5min Video: Newton’s 3rd Law https://www.youtube.com/watch?v=EgqcGrB3re8

31. Newton’s Third Law of Motion For every action (or force), there is an equal and opposite reaction (or force). Momentum – property of moving object resulting from its mass and velocity. ACTION REACTION Momentum (p) = mass x velocity

32. 11min Video: 3 Laws Review https://www.youtube.com/watch?v=kKKM8Y-u7ds

33. Quiz: Newton’s Laws of Motion ______ 1. As an ice skater pushes harder with his leg muscle, he begins to move faster is an example of a. Newton’s 1st Law b. Newton’s 2nd Law c. Newton’s 3rd Law ______ 2. When you paddle a canoe, the canoe goes forward is an example of a. Newton’s 1st Law b. Newton’s 2nd Law c. Newton’s 3rd Law ______ 3. The Law of Inertia is another name for a. Newton’s 1st Law b. Newton’s 2nd Law c. Newton’s 3rd Law ______ 4. The equation F = m x a represents a. Newton’s 1st Law b. Newton’s 2nd Law c. Newton’s 3rd Law ______ 5. According to ___ an object at rest will stay at rest unless acted upon by a force. a. Newton’s 1st Law b. Newton’s 2nd Law c. Newton’s 3rd Law

34. Quiz: Newton’s Laws of Motion Answers 1. B 2. C 3. A 4. B 5. A

35. Gravity, Weight, and Friction

36. II. What is Gravity? • Gravity is defined as a force that pulls every mass toward every other mass. • The larger the mass, the more the gravity. Since Earth is the biggest mass around, gravity pulls EVERYTHING towards the center of the Earth. • Since the Sun’s mass is greater than Earth’s, Earth is pulled around the sun.

37. II. What is Gravity? D. The acceleration caused by gravity is 9.81 m/s2. This means that each second something falls, the speed increases by 9.81 m/s

38. Gravity – any two masses that exert an attractive force on each other. Gravity depends on mass & distance between objects Weight – gravitational force exerted on an object; measured in units called Newtons The greater the object mass, the stronger the gravitational force on it

39. III. What is Weight? • We use the word weight to describe a force – weight is defined as the force created by gravity on objects. • If you know the mass of an object, you can calculate the weight by using Newton’s second law.

40. (11) What is the formula for weight? • (12) How much does a 180lb person weigh on the moon?

41. III. What is Weight? C. The formula for weight is: Force of Weight = mass x gravity’s acceleration D. Or Fw = mass x 9.81 m/s2 E. This means that you can calculate the weight of an object in any gravity situation. On the moon, because the gravitational acceleration is only 1/6th of earth’s, someone that weighed 100 lbs on the earth would weigh 17 lbs on the moon.

42. Projectile Motion Projectile – anything that is thrown or shot through air A projectile follows a curved path and has: and V E R T I C A L Motion perpendicular to Earth’s Surface MOTION Horizontal Motion Motion parallel to Earth’s surface

43. Centripetal Force Centripetal acceleration – acceleration toward the center of a curved or circular path “centripetal” means toward the center Centripetal force – force acting toward the center of a curved or circular path

44. IV. What is Friction? • Friction is a term used to describe forces that result from relative motion between objects. For example, the friction between the wheel of the car and the road. • So there is friction between ANY two things that move. • Friction is caused at the microscopic level between molecules on the two surfaces rubbing against each other.

45. Friction – the force that opposes the sliding motion of two touching surfaces. Friction is caused by microscopic bumps on surfaces called microwelds.

46. IV. What is Friction? D. Friction between two objects causes wear on each of those objects. For example, your tires get worn down on the road, and eventually the road gets worn down from the friction of the tires.

47. Air Resistance – friction – like force that opposes motion of objects that move through air – depends on speed, size & shape of object

48. VI. How Does Friction Affect Acceleration? D. Friction always reduces acceleration. This means that friction will always slow things down a little. E. All machines have some degree of friction

49. Quiz: Motion and Forces Label 4 types of friction: 1. ___________________ 2. ___________________ 3. ___________________ 4. ___________________ 5. When two or more forces act on an object at the same time it’s called a _______________________________________. 6. A friction-like force that opposes motion of objects moving through the air is called _______________________________________. 7. Friction is caused by microscopic bumps on surfaces called ___________________

50. Quiz: Motion and Forces Answers 1. Sliding 2. Static 3. Fluid 4. Rolling 5. Net Forces 6. Air Resistance 7. Microwelds