Motion, Forces, and Energy

Transcription

1 Motion, Forces, and Energy

2 What is motion? Motion - when an object changes position

3 Types of Motion There are 2 ways of describing motion: Distance Displacement

4 Distance Distance is the total path traveled. Look at the map - Is the pink dotted line or the green dotted line showing distance?

5 Displacement Displacement is the distance ONLY between the starting and ending points. It s a straight line between start and finish.

6 Distance vs. Displacement B 4m C 3m 5m A Find the distance and displacement of a person who travels from point A to B to C to A. Distance Displacement

7 Relative Motion How do you know what direction something is? Is Florida north or south? Is Alaska north or south? If you were in the Bahamas, what direction would Florida be?

8 Relative Motion Motion must have a reference point. This means you must compare the motion of an object to something else. Consider stars at night...

9 Describing Motion There are 3 main ways to measure the motion of an object. Speed Velocity Acceleration

10 Speed Speed is distance traveled divided by the time taken to travel the distance. speed (in meters/second)= distance/time s = d/t

11 Types of Speed Constant Speed - the speed at any given time will be the same. When can we achieve this? Instantaneous Speed - Speed at any instant in time What measures this for us?

12 Types of Speed Instantaneous speed is measured with a speedometer

13 Types of Speed: Average Speed - can be calculated by dividing total distance by total time

14 Calculating Speed, etc. Here is a simple way to remember how to solve speed, time, or distance problems...

15 The Magic Triangle How can we calculate speed? Speed= distance/time (D/T) Units: miles/hour, meters/second, etc. mph or m/s Distance = speed x time (SxT) Time = distance / speed (D/S) d S t

16 Example Problem #1: Find the speed, in meters per second, of a baseball thrown 40 meters in 2 seconds.

17 Answer: 20 m/s

18 Calculating Speed, Time & Distance (using the magic triangle!) Example #2. A car is traveling at a speed of 50 km/hr. How far will the car have gone in 2 hours? Show all your work!

19 Answer: 100Km

20 Practice Problem: Example # 3. Sarah backstrokes at an average speed of 8 meters per second, how long will it take her to complete the race of 200 meters length? d S t

21 Answer: 25s

22 Velocity Velocity - is speed with a direction Example - The tornado is moving 15 mph to the north east It is calculated just like speed except you must the direction in your answer!

23 Acceleration Acceleration - the change in velocity. Acceleration can occur 3 ways: Speed Up Slow Down Change Directions

24 Calculating Acceleration To calculate acceleration you must know: Final Speed Starting or Initial Speed Time

25 Acceleration Equation The equation looks like this: a= s f - s i t

26 Acceleration - BrainPOP

27 Forces An object s motion changes because of forces. A force is a push or a pull A force has a size and a direction.

28 Forces - BrainPOP

29 Forces Contact Forces- a force that is exerted when two objects are touching each other. Long-range forces- a force exerted when the objects are NOT in contact. Can you think of any examples? Examples- Gravity, Magnetism, Electricity

30 Unit of Forces Forces are measured in Newtons (N). The unit is named after Sir Isaac Newton. One Newton is roughly equal to the force it takes to lift half a glass of water.

31 Newton's Laws of Motion - BrainPOP

32 Newton s First Law of Motion An object remains at rest or moves in a straight line with a constant speed unless it is acted upon by an outside force.

33 Inertia and Mass The first law is often called the law of Inertia. Inertia = an object s tendency to resist a change in motion. It wants to keep moving or sit still. What causes inertia?

34 Adding Forces Motion depends upon the size and direction of all forces acting on an object. Balanced Forces - Forces that are equal but in opposite directions. No change in motion will occur

35 Unbalanced Forces Unbalanced Forces- Forces on an object that are either not equal or not opposite. Change in motion will occur in the direction of the greater force!

36 Newton s Second Law An object, acted on by an unbalanced force, will accelerate in the direction of the force.

37 Newton s Second Law Newton s Second Law says that the acceleration of an object can be calculated by the following: Acceleration= force (N) mass (kg)

38 Gravity Every object exerts an attractive force on every other object! Gravitational Force- the attractive force between two objects, it depends on two things: Mass (More Mass =More Gravity) Distance (Closer Together = More Gravity)

39 Gravity The acceleration due to gravity is ALWAYS 9.8 m/s 2 In other words, for every second an object falls toward Earth, its speed will increase by 9.8 meters per second. That is until air resistance and gravity are balanced forces. This point is known as Terminal Velocity.

40 Gravity - BrainPOP

41 Friction Friction- a force that resists motion between surfaces that are touching. There are 4 types of friction...

42 Static Friction Static friction is keeps an object at rest.

43 Sliding Friction Sliding Friction is the friction that occurs while an object is in motion. It typically slows down objects. When would you want to increase or decrease sliding friction?

44 Rolling Friction Rolling Friction occurs when a wheel rolls on a surface Walking is an example of rolling friction.

45 Air Resistance This is also called fluid friction. Molecules in the air (or a liquid) collide with forward moving objects. This will slow down motion. It acts as a force in the opposite direction of motion.

46 Newton s 3rd Law Forces always act in equal but opposite pairs You probably know it better, For every action there is an equal and opposite reaction!

47 Using the 3rd Law When you kick a ball a force is put on your foot and an equal one on the ball. That s why the harder you kick the more it hurts.

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49 Mass vs. Weight What is the difference between mass and weight?

50 Mass The amount of matter in an object This cannot change!

51 Weight This is the force of gravity on an object This can change... On Earth you may weigh 150 pounds, but...

52 ...On other planets Mercury Jupiter- 394 Venus- 136 Saturn- 179 Moon- 24 Uranus 133 Mars Neptune

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54 ENERGY Energy is the capacity or ability to do work.

55 Energy Two Types of Energy: Potential Kinetic

56 Unit for WORK and ENERGY JOULES or J - the SI unit used to express work or energy / equal to the work done by applying 1 Newton of force over a distance of 1 meter.

57 Two Types of Energy: 1. Potential Energy: The energy of position, or stored energy. (Example: A rock being held up off the floor)

58 Potential Energy - BrainPOP

59 Two Types of Energy POTENTIAL ENERGY FORMULA: PE = mass x g x height - mass in kilograms - g = acceleration due to gravity m/s2 - height in meters The answer expressed in Joules - J as the unit.

60 Calculating Potential Energy PE = mass x g x height If a mass that weighs 8 kg is held at a height of 10 m, what is its potential energy?

61 Calculating Potential Energy PE = mass x g x height If a mass that weighs 8 kg is held at a height of 10 m, what is its potential energy? ANSWER: 784J

62 Two Types of Energy 2. Kinetic Energy: Energy that results from the motion of an object OR particles within the object or substance (Heat / Thermal energy is a form)

63 Kinetic Energy - BrainPOP

64 KINETIC ENERGY FORMULA: KE = 0.5 x mv² m = mass in kilograms v = velocity in m/s The answer expressed in Joules - J as the unit.

65 Calculating Kinetic Energy KE = 0.5 x mv² If a 55kg runner is traveling at 3.86m/s, what is their kinetic energy?

66 Calculating Kinetic Energy KE = 0.5 x mv² If a 55kg runner is traveling at 3.86m/s, what is their kinetic energy? ANSWER: J

67 Speed, Mass, Energy Relationship SO, in the formula for Kinetic energy, what happens to the Kinetic Energy if MASS increases? (common sense) What happens to Kinetic Energy if SPEED increases? (also common sense)

68 Mass & Kinetic Energy Relationship

69 Speed/Velocity & Kinetic Energy Relationship

70 Distance / Time Graph

71 Distance / Time Graph

72 Speed / Time Graph