Presentation on theme: "Motion, Forces, and Energy"— Presentation transcript:
1 Motion, Forces, and Energy Chapter 1: Motion and Momentum
2 Section 1: What is motion? All matter is constantly in motion.
3 Motion involves a change in position… An object changes position if it moves relative to a reference point.To understand a reference point;Picture yourself standing at the front officeThen, you walk to our classroomWhen you reach our classroom, you have traveled about 50 metersSince the office is where we started, it would be our reference point, because our position has changed 50 meters relative to the starting spot (the office) and motion has occurred
4 Distance and Displacement Distance is the total length of the route an object travels when it moves.Displacement includes distance and direction of the stopping point from the starting point.
5 SpeedSpeed- the distance traveled divided by the time taken to travel the distance.Formula for speed:speed (s)= distance (d) / time (t) ors= d/tThe for speed are meters per second (m/s).An object in motion can change speeds many times as it moves from one point to another, speeding up or slowing down.
6 Average SpeedAverage speed- equals the total distance traveled divided by the total time taken to travel the distance.Question: If it takes you 0.5 h to walk 2 km to the library, what is your average speed?We solve this equation by using the s= d/t method:Plug in the numerical digits into the equationSo, 2 km/0.5 h = ?4 km/h
7 What is instantaneous speed? Instantaneous speed- the speed of an object at one instant of time.
8 How do you graph motion?Motion can be graphed on a distance-time graph with time plotted on the horizontal axis (x-axis or left to right) and distance plotted on the vertical axis (y-axis or up and down).The steeper the line on a distance-time graph, the greater the speed.A horizontal line on a distance-time graph indicates that no change in position is occurring and the speed is 0m/s.
13 Change in VelocityEach time you take a step you are changing the velocity of your body.You are probably most familiar with the velocity changes of a moving bus or car.Acceleration- change in velocity divided by the time for the change to occur; it can include an object’s speeding up, slowing down, and/or changing direction.
14 Calculating Acceleration Change in velocity = final – starting velocity velocityAcceleration= final speed- starting speed timeOr: a= (sf-si)/tAcceleration= change in velocity time
15 Calculating Acceleration (cont’d) The unit of acceleration is distance divided by time squared; (m/s2).Acceleration is positive when an object speeds up.Acceleration is negative when an object slows down.
16 A car traveling at 60 mph accelerates to 90 mph in 3 seconds. What is thecar’s acceleration?Velocity(final) - Velocity(original)Acceleration=time90 mph - 60 mph=3 seconds30 mph=3 seconds=10 mph/second
17 A car traveling at 60 mph slams on the breaks to avoid hitting a deer. The car comes to a safe stop6 seconds after applying the breaks. What is thecar’s acceleration?Velocity(final) - Velocity(original)Acceleration=time0 mph - 60 mph=6 seconds- 60 mph=6 seconds=- 10 miles per hour per second
18 Graphing Acceleration Accelerated motion can be graphed on a speed-time graph with speed on the vertical axis (y-axis or up and down) and time on the horizontal axis (x-axis or left to right).An object that is speeding up will have a line on a speed- time graph that slopes upward.An object that is slowing down will have a line on a speed-time graph that slopes downward.A horizontal line on the speed-time graph represents an acceleration of zero or constant speed.
35 Mass and Inertia Mass- the amount of matter in an object. The SI unit for mass is the kilogramInertia- the tendency of an object to resist a change in its motion.Objects with more mass have more inertia, thus is harder to change its motion
36 MomentumMomentum- a measure of how difficult it is to stop a moving object; equals the product of mass and velocity.Momentum is usually symbolized by pMomentum= mass X velocity orp= mvMomentum has units of kg multiplied by m/sSince velocity includes direction, momentum has the same direction as velocity.
37 Law of Conservation of Momentum Law of conservation of momentum- the total momentum of objects that collide with each other does not change.
38 There are many types of collisions… Objects stick together and move still stuck together, although possibly at different speeds.
39 Types of collisions (cont’d) Two objects bounce off each other when they collide, and may transfer momentum from one to the other.In both cases, the total momentum of the objects that collide is the same before and after the collision.
40 You know what’s coming…(Math Equations!) hill.com/sites/ /student_view0/chapter1/mat h_practice_3.html
41 Practice Problem 1Calculate the momentum of a 16-kg bicycle traveling north at 3 m/s.