Motion

1. Motion

2. What is motion? The change in position of an object over time Objects may change their motion in many ways. We will study the different kinds of motion objects have. What is the study of Motion? Kinematics What is the difference between distance and displacement? Distance is simply how far something has moved. Displacement is not quite this simple. Displacement involves direction and is the relative distance from the starting point. What does this mean???

3. Consider the following diagram: What is the total distance traveled by this person from their starting point to their current position? The distance is 80 meters. Distance What is the displacement of this person? The displacement is the position of the person when compared to the starting point Displacement Displacement = 20 meters.

4. What are examples of types of motion? Speed is one example. Speed is a very important type of motion. Who has the fastest bicycle? Who runs the fastest? Who has the fastest car? Which animal runs the fastest? Which airplane will get from point A to point B fastest? Consideration of speed is all around us. People have abused the speed of cars and limits have been placed on the speed of cars. Speed can KILL. Speed can be exhilarating. Speed is a type of motion.

5. What is speed? Speed is a rate of change of position. Speed can be calculated. How do you calculate speed? Speed is equal to the distance divided by the time. Speed may have various units. These units come from the formula. If the distance is measured in miles and the time measured in hours, the unit of speed is d t S = miles hour miles per hour We often use metric units and measure distance in meters and time in seconds, so the unit is m cs meters per second

7. What is the difference between speed and velocity? Speed is simply the distance traveled per unit time. Velocity is speed PLUS another component – direction Speed is how fast a body is moving. Velocity is how fast a body is moving AND in which direction. Speed only gives the magnitude (how big or how small). Velocity give both magnitude and direction. 65 miles/hour is speed 65 miles/hour North is velocity

8. What is instantaneous speed? Instantaneous speed is speed at a specific point in time. In your car, the speedometer measures instantaneous speed. The graph below may represent a typical trip on a bike. A single point on this graph would represent instantaneous speed In real life, your instantaneous speed usually changes as you travel from one place to another. Speeding up and slowing down occurs because of traffic and/or terrain.

9. Average speed is determined by dividing the total distance by the total time.

10. Kinematics Example #1 What is the speed of a car in miles/hour if it covers 200.0 meter (m) in 8.10 sec? Converting complex units can be tricky, unless you know how to use conversion factors. Follow these steps carefully and pay attention to the order of the steps. 1.00 miles 200.0 meters 8.10 seconds seconds 3600.0 X X hours meters 1.00 1609 Put “seconds” in here because we need to cancel this unit. Remember that in a conversion factor, the numerator = the denominator. 1 mile = 1609 meters Conversion Factor: 1 hour = 3600 seconds Notice that “meters” goes on the bottom because we need to cancel this unit 55.2 miles/hour Now we need to cancel the units!

11. Kinematics Example #1 55.2 mph 

12. Kinematics Example #2 On a trip, you travel at 25.0 mph for 30.0 minutes, hit the highway and go for an hour at 70.0 mph, stop at a rest stop for 10.0 minutes. Find your averagespeed!

13. Kinematics Example #2 Average speed = total distance total time How do you solve this? There are three different speeds in this problem. For each section find the distance and time. Then add the distances to find the total distance and add the times to find the total time.

14. Kinematics Example #2 Segment 1: 25 mph for 30 minutes Time = 30 min or 0.5 hours Distance = velocity X time = 25 X 0.5 hours Distance = 12.5 miles Segment 2: Total time = 1 hour Distance = 70 miles Segment 3: Total time = 10 minutes X = 0.17 hrs Distance = 0 Total Distance = (12.5 + 70 + 0) miles = 82.5 miles Total time = (0.5 + 1.0 + 0.17) hours = 1.67 hours

15. Kinematics Example #2 Vavg = = 49.4 mph Vavg =

16. Motion Graphs – graphs provide a visual way of seeing motion. We’re going to look at two kinds of graphs distance – time graphs velocity – time graphs This is a distance – time graph because the x-axis measures distance and the y-axis measures time. x-axis y-axis

17. The slope of the line on a distance-time graph represents the velocity of an object. Zero velocity Zero velocity Slower positive velocity The average velocity may be calculated by dividing the total distance by the total time: 300 cm / 20 seconds 15 cm/s High positive velocity Zero velocity

18. Speed-time or velocity-time graphs are more difficult to comprehend. Zero acceleration Constant positive acceleration Constant negative acceleration First 3 seconds – 0 velocity & 0 acceleration 3-4 secs – increasing velocity & constant acceleration 4-6 secs – constant velocity & 0 acceleration 6-7 secs – decreasing velocity & constant (-) accel. The slope of the line on a velocity-time graph represents the acceleration of the object.

19. What is acceleration? Acceleration is a change in velocity in a certain amount of time. For example, if someone speeds up from 5 meters per second to 10 meters per second in 10 seconds, he or she accelerates. Acceleration may be calculated using the following formula: a = Vf – Vi t Vf is final velocity Vi is initial velocity t is the amount of time in which the change occurred. So in the example above: a = 10 m/s – 5 m/s = 0.5 m/s/s 10 seconds 0.5 m/s2 The unit for acceleration is almost always m/s2.

20. This is a negative acceleration since the final velocity is less than the initial velocity. Calculating positive acceleration: Suppose an airliner travels in a straight line down the runway and changes velocity from a stopped position to 80 m/s in 20 seconds. What is the acceleration of the airliner? Calculation negative acceleration: A skateboarder is moving in a straight line at 3 m/s slows to a stop in 2 seconds. The final velocity is 0. What is the acceleration?

22. How do motion and forces relate? What is a force? A force simply is a push or pull. pull push

23. A force can cause motion only if it is met with an unbalanced force. Forces can be balanced or unbalanced. Unbalanced forces cause motion. Balanced forces cause no motion.

24. Inertia The tendency of an object to resist a change in motion. A body in motion tends to want to remain in motion. A body at rest tends to want to remain at rest. At Rest In Motion

25. Do you remember the balloon demonstration from last chapter? Remember the balloon went to the right when the driver turned right and the balloon went backward when the vehicle stopped. The balloon went forward when the car accelerated. WHY? Because of Inertia!!!! See the video again in Module 1. Why did the balloon appear to contradict inertia??? It really did not contradict inertia. The air in the vehicle compartment (more dense than the balloon) was more greatly affected by inertia that the balloon. When the car turned right, the air in the compartment went to the left, forcing the balloon to move right. When the car stopped, the air in the compartment moved forward because of inertia, causing the balloon to move backward. Inertia!!!

26. When you are moving fast around a curve, your body tends to want to move toward the curve because of inertia. You tend to want to keep going straight. When you accelerate from a stopped position, your body lunges back some. This is because your body was at rest and tends to want to remain at rest when you accelerate. When you come to a stop, your body tends to lunge forward because your body tends to want to keep moving forward. This is all inertia!!!! View the seven examples of inertia in this video. You might also want to watch this video!

27. What are Newton’s Laws of Motion?? Isaac Newton developed three laws of motion that are still strongly adhered to in our day. Newton’s First Law of Motion - An object moving at a constant velocity keeps moving at that velocity unless a net force acts on it. On Earth objects stop moving most of the time because of the force of friction or gravity acting on it to cause it to stop. Newton’s First Law of Motion is often called the Law of Inertia since they are closely associated.

28. What are some examples of Newton’s 1st Law? A marble rolling on a flat surface at constant velocity will eventually slow down (change its velocity) because of the force of friction opposing it. An arrow shot into the are with an initial constant velocity will change it’s velocity (slow down) due to the opposing force of gravity. A person sitting in their car with no motion (constant velocity of zero) will change velocity when the force of the car’s engine accelerates the car forward.

29. What is Newton’s Second Law of Motion? A constant force acting on an object will cause the object to have a constant acceleration. This law is represented by the following mathematical formula: Force = mass x acceleration (or) F = ma The SI unit of force is the Newton (N) 1 N = (1 kg)(1 m/s2) The English unit of force is the pound (lb) 1 pound = 4.45 Newtons

31. What is Newton’s Third Law of Motion? For every action force, there is an equal but opposite reaction force. (also commonly know as “for every action there is an equal but opposite reaction”) Read the information at this link about Newton’s Third Law of Motion. Read also the next page of information at the same site.