Forces and Motion

1. Forces and Motion

2. Motion • What do you think it means to be in motion? How can we tell if something is in motion?

3. Motion • Motion: a change in position, measured by distance and time. 

4. Motion • Determining if an object changes position requires a frame of reference. The Earth is the most common frame of reference

5. Speed • Speed: the distance traveled by a moving object per unit of time To calculate speed, use the equation Speed = distance / time • Speed only gives distance and time!

6. Average Speed • Average speed: the speed of moving objects is not always constant • To calculate average speed you look at total time and distance Average speed = total distance / total time

7. Average Speed • 1. What is your average speed if you take 2h to jog 8 miles ? • Speed= distance/ time • 8m/2h= 4 mph • 2. What is the average speed of a car if it travels 500 miles in 20 hours? • Speed= distance/ time 500m/20h = 25 mph

8. Velocity • Velocity is speed in a given direction. • Velocity gives distance, time, and the direction of travel. • Velocity changes by changing direction or changing speed!

9. Scientists have a special way to measure a change in velocity: Acceleration Acceleration is a change in velocity. NSF North Mississippi GK-8

10. Acceleration • The change in velocity/the time it takes for the change to occur Acceleration = (final velocity – initial velocity) time Velocity is measured in m/s and time in seconds.

11. Calculating Acceleration A roller coaster’s velocity at the top of the hill is 10 m/s(initial) Two seconds later its velocity is 26 m/s (final). What is the acceleration of a roller coaster? Acceleration= final velocity- initial velocity time Accel= 26m/s -10m/s = 16 = 8 m/s/s 2 2

12. If you’re speeding up, you have positive acceleration. If you’re slowing down, you have negative acceleration. If you’re changing speed quickly, you have high acceleration. If you’re changing speed slowly, you have low acceleration. The Way Acceleration Works: NSF North Mississippi GK-8

13. True or false? • If you slow down on your bicycle, you accelerate. • If you ride your bicycle at a constant speed, you cannot accelerate. • Changing the speed and changing the direction of your bicycle are both examples of acceleration.

14. Example: You’re driving along in your car and suddenly have to slam on your brakes for a red light. Negative or positive acceleration? High or low acceleration? High negative acceleration because you’re slowing down quickly. NSF North Mississippi GK-8

15. p v m Momentum • Momentum • The measure of how difficult it is to stop a moving object p = mv p: momentum (kg ·m/s) m: mass (kg) v: velocity (m/s)

16. Calculating Momentum • A 20,000 kg ship is traveling east at 20 m/s. What is the momentum of the ship? • P=mv • 20,000 kg X 20 m/s = • 400,000 kg* m/s

17. Law of conservation of momentum • According to the law of conservation of momentum: the total momentum of objects that collide will be the same before and after the collision. • Momentum will not be lost during the collision.

18. Quick Review Velocity: speed of motion Acceleration: change in velocity Momentum The measure of how difficult it is to stop a moving object NSF North Mississippi GK-8

20. Force Force: any push or pull

21. Forces are measured in _____ A _____ is the combination of all of the forces acting on an object.

22. Forces

23. Balanced Forces forces acting on an object that are opposite in direction and equal in size no change in velocity Force

24. Balanced vs. Unbalanced Forces Balanced forces will not cause a change in the motion of an object; they have a net force of zero N. • Examples of balanced forces are: • 1. ______, 2. _____, 3. _____ .

25. Balanced vs. Unbalanced forces • Unbalanced forces could be best described as __________________________ . • Examples of unbalanced forces are ___________________________ .

26. Force Drawing • Create a drawing that shows an example of balanced forces. The drawing should show the forces acting on the object and what happens to the object if the forces become unbalanced.

27. Forces

28. Forces • You and a younger brother or sister are at a neighborhood pool. Your brother or sister asks why there are signs that say “NO RUNNING!” What would be your answer?

29. Forces • _____ , ______ , and ______ are examples of common lubricants. • Therefore, it is easier to slip when there is water on the floor because the water acts as a ______ that lessens the friction between the bottom of your shoe and the floor.

30. Pushing pedals, pressing brakes, and kicking soccer balls are all examples of forces. A force is anything thatchanges the velocity of an object. But what’s a change in velocity? A change in velocity is acceleration, so . . . A force is anything that gives an object acceleration. NSF North Mississippi GK-8

31. Friction • _____ is a force that opposes motion between two surfaces that are in contact. • A _____ is a substance that lessens friction.

32. Friction • Friction • force that opposes motion between 2 surfaces • depends on the: • types of surfaces • force between the surfaces • A _____ is a substance that lessens friction.

33. Friction • There are four types of friction.

34. Friction • Four Types of Friction • Static Friction – force that acts on objects that are not moving. (Couch Potato) • Sliding Friction - force that opposes the direction of motion of an object as it slides over a surface. (Ice skating or bobsledding) • Rolling Friction – friction force that acts on rolling objects. (Rollerblading) • Fluid Friction – force that opposes the motion of an object through a fluid. (Planes flying or submarines traveling)

36. Friction • Write a story that describes what a day in your life would be like if there was no friction.

37. Gravity

39. Gravity • Isaac Newton discovered the ______ ______ of Gravitation. • Gravity acts on any objects with mass. Example: You and your books, pencils, paper, etc.

40. Universal Law of Gravitation • Mass and gravity have a directly proportional relationship. • The distance between the centers of masses of the two objects and gravity have an inversely proportional relationship.

41. Differentiate between Mass and Weight. • Weight is dependent upon the acceleration due to gravity on a particular planet. • For instance: g on earth is 9.8 m/s² • The larger the planet, the _____ the gravitational force.