Motion notes Physical Science

Are you moving? Something is in motion if it changing position Determining whether something changes position requires a point of reference Frame of reference = a place or object that you assume is fixed. You observe how objects move in relation to that frame of reference. Relative motion =how are you moving relative to a frame of reference

Distance and Displacement Ex. Suppose you are going to school and you need to be there in 5 mins. Can you get there on time by walking or should you ride your bike? You need to know the distance you need to travel and the direction. You would specify your displacement

Distance Distance :is a measure of how far an object has moved and is independent of direction. If a person travels 40m due east, turns and travels 30m due west, the distance traveled is 70m.

Displacement Displacement : has both magnitude (measure of the distance) and direction. Displacement is a change of position in a particular direction. For example: 40m east is a displacement.

Total Displacement Total or final displacement: refers to both the distance and direction of an object’s change in position from the starting point or origin. Displacement only depends on the starting and stopping point. Displacement does not depend on the path taken. If a person travels 40m due east, turns and travels 30m due west, the total displacement of the person is 10m east. If a person travels 40m east and then travels another 50m east the total displacement is 90m east.

Example Total Distance = 4m + 3m = 7m Displacement = distance of most direct route + direction Displacement = 5m northeast

Speed To describe motion: how fast something is moving Speed = Distance (in meters) S = _D_ Time (in seconds) T D = S X T T = _D_ S D T S

Example Ex. Calculate the speed of a swimmer who swims 100 m in 56 seconds. S = d/t S = 100m/56 sec. S = 1.8 m/s *Don’t forget your units!!

Average vs Instantaneous Speed How can you determine a car’s speed if it is always changing? Ex. Car travels fast on the express way but slows down for a red light. Answer = Calculate its average speed between where it starts and stops. The speed of an object at one instant of time is the object’s instantaneous speed. What is the difference between average and instantaneous speeds?

Average vs Instantaneous Speed Ex. It takes you 0.5 h to walk 2 km to the library. Your average speed would be as follows: Speed = total distance/total time taken S = 2km / 0.5 h S = 4 km/h However, your instantaneous speed probably changed throughout your trip. At a crosswalk your speed was 0 km/h, then you sped across the highly traffic street at 7 km/h. Then everywhere else you walked at a steady pace of 4 km/h A speedometer measures instantaneous speed.

Mini -Activity: Speed Walking Materials Stopwatch What To Do 1) The tape on the floor marks 5 meters long. 2) Time how fast you can walk the length of one tape line to the next without lifting your feet from the floor. 3) Repeat three times. 4) Record your data & calculate your average speed. Moon walking bird: http://www.youtube.com/watch?v=eI_quJRRGxk

Data Trials Time (seconds) 1 2 3 Average time Average speed = distance / time

Graphing Motion -Time goes on the x-axis - Distance goes on the y axis You can use a distance-time graph to compare speeds of objects. What student is the fastest? _D__ What student is the slowest? _A__ A steeper line represents a Greater speed A horizontal line means no change in position therefore speed equals zero.

Speed graph When the line is horizontal on a speed graph the object is not moving. - Motion of Earth’s crust—so slow we don’t notice A steady line up is constant speed Ex. The speed of light is always at constant speed A curved line up is increasing speed

Speed graph Observe the red line, describe the object’s speed and what it is doing. Answer: The line is increasing = car starts its journey away from home. The horizontal line = car stops at a store The line is decreasing = car is going home

Velocity Velocity: the speed of an object and the direction of its motion. Ex. Car is moving west with a speed of 80 km/h or V = 80 km/h west The velocity of an object is sometimes represented by an arrow. The arrow points in the direction in which the object is moving. The velocity can change even if the speed stays constant Ex. Speed is 40 km/h but direction goes from west to north.

Calculating Velocity Velocity is a vector quantity, it has a direction!

Calculating Velocity In the equation, “v” can represent either velocity or speed and “d” can represent either displacement or distance, depending on the context of the problem. Speed and velocity video clip 2:36 https://www.youtube.com/watch?v=-6lrr6-ADY0

Calculating Velocity When calculating average velocity using v =d/t: the average velocity equals the total displacement divided by the total time. The total displacement may be different from the total distance. * When indicating the average velocity, direction must be given and the average velocity will have the same direction as the total displacement. The moving man simulation http://phet.colorado.edu/en/simulation/moving-man

Acceleration Acceleration = The rate of change of velocity and occurs when an object changes its speed, its direction, or both. -Positive acceleration = speed increases. - Negative acceleration = speed decreases

Acceleration When an object changes speed or direction, it is accelerating. Examples: 1. Earth is accelerating constantly as it orbits the sun in a nearly circular path.

Calculating Acceleration Calculation for acceleration: Acceleration = change in velocity (Δ V) Time Change in velocity = Final velocity – Initial velocity SI units for acceleration = meters/second/second = m/s2 (meters per second squared).

Calculating Acceleration Example Amusement park acceleration—Roller coasters 1. Changes in speed cause acceleration. 2. Changes in direction cause acceleration.

Calculating Acceleration Example Example: Calculate the acceleration of a bus whose speed changes from 6 m/s to 12 m/s over a period of 3 seconds. A = Δv/Δt A = (sf – si) t A= (12- 6)/ 3 = 6 ÷ 3 = 2 m/s2

Graphing acceleration The motion of an object that is moving in a single direction can be shown with a graph. Speed is on the y-axis and time is on the x-axis. From A to B and C to D you will have a positive acceleration From B to C you have zero change in speed From D to E you will have slowed down

Collisions Collision = when two moving objects collide. Ex. When a cue ball collides with another ball in a game of pool. What happen? The collision can change the speed of each ball, the direction of motion of each ball, or both. The changes of motion depend on their masses and their velocities before the collision.

Mass and Inertia Mass = the amount of matter in an object. The more mass an object has, the harder it is to change its motion. Ex. You would have to push harder to stop and adult than to stop a child. Inertia = the tendency of an object to resist a change in its motion The amount of resistance to a change in motion increases as an object’s mass increases. Show penny/card/cup demo Bill Nye Motion and interia 23:16 https://www.youtube.com/watch?v=TGuhXTJgsqc Questions  1. To which object was a force applied by the flick and which object was not acted upon by the flick? 2. Why did the penny fall into the cup and not fly off with the index card? 3. What force held the penny in place while the card was flicked out? What force brought the penny down into the cup? 4. Would the penny move in the same way if sandpaper was used instead of the index card?   Summary The inertia of every object resists the change in motion. In this case, the inertia of the penny held it in place while the index card was flicked out from under it. The force acting on the index card was not applied to the penny. After the index card was moved from under the coin, gravity supplied the force to bring the penny down into the cup. If a force had been applied to both the card and the penny, then both would have moved and the penny would not have fallen into the cup.

Momentum Besides increasing the mass, increasing the speed or velocity makes an object harder to stop. Momentum = a measure of how hard it is to stop an object it depends on the object’s mass and velocity. Represented by p Momentum (kg ·m/s) = mass (in kg) X velocity (in m/s) p= m·v *Since velocity includes a direction, momentum has that same direction

Momentum example Ex. Calculate the momentum of a 14 kg bicycle traveling north at 2 m/s. p = m · v p = (14 kg) X (2 m/s) p = 28 kg · m/s Bill Nye : momentum 22:56 https://www.youtube.com/watch?v=217dpIeuPVQ

Conservation of Momentum In billiards when the cue ball hits another ball, the cue ball slows down and may change direction. Meanwhile, the other ball starts moving, so its momentum increases. In any collision, momentum is transferred from one object to another. The momentum lost by one ball equals the momentum gained by the other ball. The total amount of momentum doesn’t change and is conserved.

The Law of Conservation of Momentum The law of conservation of momentum: the total momentum of a group of objects remains constant unless outside forces act on the group Only an outside force, such as friction between the billiard balls and the table, can change the total momentum of the group of objects. Friction causes the balls to slow down therefore momentum will decrease

Using Momentum Conservation After the collision, the total momentum remains the same, and only one object is moving. Its mass is the sum of your mass plus the mass of the basketball. Use the equation to find the final velocity Total momentum = (mass of girl + mass of basketball) X velocity 10 kg · m/s east = (2 kg + 48 kg) X velocity 10 kg · m/s east = (50 kg) X velocity 0.2 m/s east = velocity Notice the final velocity is much smaller.

Using Momentum Conservation Ex. A 48 kg Girl on roller skates at rest, catches a thrown 2-kg basketball at a velocity of 5 m/s east. What is the initial momentum? Total momentum = momentum of basketball + your momentum Pt = 2 kg X 5 m/s east + 48 kg X 0 m/s Pt = 10 kg · m/s east

Types of collisions Masses in these cases are all the same.

Types of collisions

Motion Bill Nye video on Motion 23:16 https://www.youtube.com/watch?v=iG-d5n9ZetM Force and motion grinch song 4:21 https://www.youtube.com/watch?v=WcoYeNbyqvw Friction: https://www.youtube.com/watch?v=nmnzLW6YoF0 Momentum: https://www.youtube.com/watch?v=217dpIeuPVQ Gravity: 22:55 https://www.youtube.com/watch?v=5S9l_eqjn_U Buoyancy 22:31 https://www.youtube.com/watch?v=zvRJ9FKTdC8 Pressure: 23:08 https://www.youtube.com/watch?v=DIYovDooemo