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1 2012 ppt semester 1 matching review
1.
2. The slides used in this video are color coded. If
you are experiencing difficulty with one aspect of
your understanding than another you might find
this coding…
useful!
Slides with
Slides with tan
red
backgrounds
backgrounds involve
involve word matching Slides with
green
problems.
concepts.
backgrounds
Slides with olive involve
backgrounds
graphing.
involve reading
data tables.
3.
4. •
Displacement
Velocity
Acceleration
Inertia
Force
Momentum
•
•
•
•
•
The change in the rate or
direction of motion.
The resistance to a change in an
object’s current state of motion.
A change in position.
A push or a pull that tends to
accelerate an object.
The movement of an object in a
specific direction over time.
The product of mass times
velocity.
5. Displacement is a change in position.
Velocity is the movement of an object in a
specific direction over time.
Acceleration is the change in the rate or direction
of motion of an object.
Inertia is the resistance to a change in an object’s
current state of motion.
Force is a push or a pull that tends to accelerate an
object.
Momentum is the product of mass times velocity.
32. Motion Map
Force Diagram
Position (ΔY) Graph
Velocity (Vy) Graph
Can you predict the
motion map, and
kinematic graphs for
this freefalling object?
Acceleration Graph
34. Motion Map
Force Diagram
Position Graph
Velocity (Vy) Graph
Can you predict the
motion map, and
kinematic graphs for
this elevator?
Acceleration Graph
36. Motion Map
Force Diagram
Position Graph
Velocity (Vy) Graph
Can you predict the
motion map, and
kinematic graphs for
the ENTIRE TRIP?
Acceleration Graph
38. Because of this wind, a 15 kg
package is blown from Dr. Fiala’s
arms and onto the ground. The 15 kg
package reaches a velocity of 30.41
m/s in a time of 4 seconds. Find the
force acting on the box horizontally if
there is no friction.
39. Force
Diagrams
Motion Map
Match the force
diagram to the motion
map. Can you also
predict the slope
shape and orientation
of the position,
velocity, and
acceleration graphs?
41. Force
Ff = 0 N
Diagram
Motion Map
Fs = 147 N
Fa = 117.79 N
Fg = 147 N
Position
Graph
Velocity
Graph
31.4
m/s
62.8
m
4s
Acceleration
Graph
7.85
m/s2
4s
4s
42. Force Diagram
Motion Map
Position (ΔY) Graph
Velocity (Vy) Graph
Can you predict what the
force diagram, and
vertical kinematic graphs
for this freefalling object?
Acceleration Graph
44. Force
Vector Arrows for this
Projectile
Position
Velocity
Using these vector arrows can
you predict what the position,
force, velocity and acceleration
vector arrows would look like
for this projectile at the start
and at the top?
Acceleration
Welcome to the physics review for semester one. Hello everybody, this is Dr. Fiala. The tutorial you are about to begin is comprehensive. Material reviewed includes Kinematics, force, projectiles, momentum and impulse. To receive the most benefit from this video there are two important points that should be noted.
Point one. I have color coded the slides so you can more easily practice skills with which you have difficulty. This is a good way for you to roll up your sweatpants. Word problems are presented on red slides. Data tables can be found on olive slides. Green slides work you graph reading skills and tan slides match concepts. Solutions are presented for each problem on the following slide. I will give you an audio cue that the slide will be changing. That way if you want to stop the video before you see the solution you can do so at that time. You may choose to view the entire video or simply move to the slide color representing your weakness.
Point two. You must have all of the formulas handy while going though the semester on physics review. If you have them written down in my order it would be helpful because I refer to the formulas as formula one, formula two, formula three and so on according to the order in which they appear on my card. Because all students must use the formula given out on final exam day, it is important that you are skilled at finding any variable in any formula. You can stop this video at any time and I encourage you do do so. I suggest that you complete this video review and tutorial when you can think about what we are talking about without distraction. Stay positive . You can do this!
To improve math skills it is important to recognize the symbols we use to represent physics quantities. Examples of this are ΔX to represent a change in position, and lower case ‘a’ to represent acceleration. However it is truly important to understand what each of those physics quantities mean. The first step to this understanding is to take the time to learn the definition of each physics quantity.
As we learn new physics quantities write them down. Study them by simply reading them after school. You will improve your math skills if you do.
Then go over their meaning when asked to find that quantity during a quiz or exam. For example if I am asked to find the velocity of an object that travels from 1 m to 3 m in 3 seconds, it might be nice to remember that velocity is the movement of an object in a specific direction over time. The word over means divided by so in this case the definition gives you the formula of the movement of three meters divided by 3 seconds is the velocity.
The vertical position graph of this projectile is parabolic. That means there will be more than one slope. Reading that kind of graph is not a problem because we simply read one slope at a time. With that in mind reading the first slope of the position graph out loud reveals a positive changing velocity from fast to slow.
Since this is positive changing velocity the slope of the velocity graph will have to be in the 1st quadrant and will be sloping towards the x-axis. I know that because nothing is slower than 0 m/s and 0 m/s is found on the x –axis. The object is slowing down while traveling to the right. This leaves us with two possibilities. Lets see if reading the second slope on the position graph sheds any light on which of these two choices is correct. The second slope is read as negative changing velocity from slow to fast.
This means the correct choice can only be the graph on the bottom right. Now I can read the slope made by those two slopes put together. Here I indicated it by a yellow arrow. I would read this out loud as constant because it is a straight line, negative because it has a downward slope, acceleration because that is the quantity that is measured by the slope of a velocity versus time graph.
The only graph that has a slope shape and orientation that reads as constant negative acceleration is the center graph.
The negative acceleration is due to gravity, which works against the velocity that is taking the projectile away from the Earth until there is no positive velocity remaining. Since the only force acting on a projectile is due to gravity, the projectile immediately begins to return to Earth with increasing velocity. Since the object is falling we agreed to refer to the velocity as negative. When velocity changes from positive to negative, in other words crosses the x-axis, the object has changed directions. Whenever an object changes directions the position graph is parabolic. Whenever the position graph is parabolic there is acceleration present. Remember that acceleration causes the shape of the position graph’s slope to be curved.
Vector arrows can be used to represent any of the vectors we have studied so far, displacement, velocity, acceleration, force, and momentum. When we use the vectors arrows as a motion map we are showing the movement of an object. The arrow heads indicate direction of motion and the length of the arrows indicate the relative amount of motion. So this motion map illustrates an object moving to the left first slowing down then speeding back up. We could also say the object went from fast to slow to fast. Lets first look at all of the position graphs that fit this motion.
The object is moving to the left. So I circled the only graphs that show movement to the left if it is read as a position graph. Now consider that the object is changing velocity according to the changing length of the motion map arrows. Fast to slow to fast. That means the slope of the position graph has be a curved line. A straight line would mean constant velocity but having acceleration automatically means changing velocity. Fast to slow to fast. The slope of an object moving at the speed of light would be vertical. So something moving fast would have a more vertical slope. That means something moving slow would have a more horizontal slope.
Reading this position graph is broken down into two slopes circled in red. The first slope is read as negative changing velocity from fast to slow. Since this slope is negative the slope of the next kinematic graph must be in the 4th quadrant. I have circled those two for you in blue. Again let’s see if reading the second slope, also circled in red, of the position graph gives us an insight into predicting the velocity graph.
Reading the second slope of the position graph illustrates an object that continues to move left but is picking up velocity. In other words, moving from slow to fast. I have place yellow arrows to indicate the direction of the slope of the velocity graph. This gives the direction of the acceleration. Can you now pick out the acceleration graph?
There must be acceleration for an object to speed up or slow down or change direction. Since the direction of the object did not change, it traveled to the left, a negative movement, the only acceleration that could slow it down was positive. Remember that opposite signs on velocity and acceleration cause an object to slow down. Then since the object still had negative velocity, in other words moving to the left, the only acceleration that can speed the object back up is negative. Like signs on the velocity vector and the acceleration vector cause an object to speed up.
This motion map illustrates an object that moved to the left slowed down, stopped, changed directions and sped back up. My knowledge of kinematic graphing tells me that the slope of the first graph will be negative because the object is traveling left, then positive because the object is traveling right and will be curved twice because it changed velocity twice. Be careful here because two curves can sometimes appear as one big curve.
Now lets see if the vector arrows tell us anything about the orientation and shape of the velocity versus time slope . For purposes of this slide only I use the color blue for left or negative and the color red for right or positive. So I am looking to match a pattern of left or negative getting slower then becoming right or positive and getting faster.
Now lets see if the vector arrows tell us anything about the orientation and shape of the velocity versus time slope . For purposes of this slide only I use the color blue for left or negative and the color red for right or positive. So I am looking to match a pattern of left or negative getting slower then becoming right or positive and getting faster. The graph located in the top row center column fits the description.
Now lets take a look at the orientation and shape of the slope of the velocity versus time graph. I can see we have constant positive acceleration.
Read all of the slopes out loud for practice. The position graph shows negative changing velocity from fast to slow followed by positive changing velocity from slow to fast. The velocity graph shows positive constant acceleration. The acceleration graph shows constant or neutral jerk. Jerk is a quantity that you will not have to calculate. Read the area of the velocity and acceleration graphs. The area of the velocity graph shows decreasing displacement to the left followed by increasing displacement to the right. The area of the acceleration graph shows constantly increasing positive velocity.
Now we have an object that is starting from rest and speeding up to the right. Displacement is on the y-axis of the position graph so moving to the right is up on the graph. We would expect to see a curved line since the object is speeding up. On a position graph a horizontal slope means slow and a vertical slope means fast. So we are looking for a slope going from horizontal to vertical.
Read the slope of the position graph out loud to determine the orientation and shape of the velocity graph. Again look at the vector arrows to help you with your verbiage. Positive movement from slow to fast. Positive means it will be found in the 1st quadrant. Of the graphs above identify the ones that are found entirely in the 1st quadrant.
Here are the graphs that have slopes starting in the 1st quadrant. Two of them marked in orange can be eliminated because they are curved. In this physics class the velocity graph will never be curved. One of the graphs can be eliminated because it has a horizontal slope indicating no change in velocity. This graph is circled in green.
So now we know what the velocity graph will look like. I have placed an arrow in the direction of the slope. Read it out loud and pick an acceleration versus time graph that would match.
The motion map indicates that an object starts from rest and speeds up to the right. The position graph is read as positive changing velocity from slow to fast. The velocity graph is read as constant positive acceleration. The acceleration graph is read as neutral or no jerk.
Here is the motion map of the object moving at constant velocity to the right. Predict what the force diagram would look like.
For an object to move at constant velocity, remember that 0m/s is a constant velocity, the sum of all forces in the x and y must equal zero. Now predict what the position, velocity and acceleration graphs would look like.
The motion map depicts an object moving to the right at constant velocity. The position graph is read as constant positive velocity. The velocity graph is read as neutral acceleration. The acceleration graph is read as neutral jerk.
The motion map of my car and occupants shows that we are speeding up to the right. We must have an unbalanced force to the right for this to occur. Since the car is not rising up off the road nor burying itself into the road, the sum of all forces on the y-axis must be zero.
The motion map of my car and occupants shows that we are speeding up to the right. We must have an unbalanced force to the right for this to occur. Since the car is not rising up off the road nor burying itself into the road, the sum of all forces on the y-axis must be zero.
A read of the position graph slope reveals the car has positive changing velocity from slow to fast. The velocity graph slope is read as constant positive acceleration. The slope of the acceleration versus time graph is read as positive constant jerk.
Since the only force acting on this object is gravity, the object is said to be a projectile in free fall. The motion map should have the object starting from rest and gaining velocity on the way down. The position graph slope should show an object falling and being displaced at an increasing rate. The velocity graph slope should be in the 4th quadrant because the velocity is negative. The acceleration graph slope should indicate that the acceleration was due to gravity.
Keep practicing your graph reading out loud.
The force diagram shows an unbalanced force upward. . The force of gravity is less than the force of support. This diagram could explain an elevator slowing down on the way down or speeding up on the way up. In this case the motion map should have the object speeding up on the way up. The position graph slope should show an object traveling upward and being displaced at an increasing rate. The velocity graph slope should be in the 1st quadrant because the velocity is positive. The acceleration graph slope should indicate that the acceleration was positive because positive velocity and positive acceleration cause an object to sped up.
Again, keep practicing your graph reading out loud to improve your ability.
This force diagram shows an unbalanced force in the vertical. The force of support is less than the force of gravity. This diagram could be from an elevator slowing down on the way up or speeding up on the way down. In this case the motion map should have the object slowing down on the way up. Since we need to pick graphs for the entire trip we will need the position graph slope to show an object traveling upward and being displaced at an increasing rate and then at a decreasing rate. The velocity graph slope should be in the 1st quadrant because the velocity is positive. The acceleration graph slope should indicate that the acceleration was positive because positive velocity and positive acceleration cause an object to sped up.
Keep practicing your graph reading out loud.
Yf = -15 m Yi = 0 m m = 15 kg g = -9.8 m/s2 Vi = 0 m/s Vf = 31.41 m/s
ti = 0 s ti = 4 s
a =
F =
The motion map of the box shows that it is speeding up to the right. We must have an unbalanced force to the right for this to occur. Since the box is not rising up off the ground nor burying itself into the ground, the sum of all forces on the y-axis must be zero.
A read of the position graph slope reveals the car has positive changing velocity from slow to fast. The velocity graph slope is read as constant positive acceleration. The slope of the acceleration versus time graph is read as positive constant jerk. Now I want you to complete these graphs by adding the magnitudes of forces, displacement, velocity and acceleration.
The force of gravity acting on an object is found by multiplying mass times the acceleration due to gravity. The force of support is equal and opposite since the box is not accelerating in the vertical. The slope of the position graph can be described by the beast formula in the horizontal. Velocity is found by using Vf = Vi + at. We have already found the acceleration in a previous slide.
In the vertical the motion map should have the object starting from rest and gaining velocity on the way down. In the horizontal the motion map should have the object having constant horizontal velocity for the entire trip. The position graph slope should show an object falling and being displaced at an increasing rate. The velocity graph slope should be in the 4th quadrant because the velocity is negative. The acceleration graph slope should indicate that the acceleration was due to gravity.
Here are the correct answers. Keep practicing your graph reading out loud.
Use one vector arrow to represent the direction of the force at the beginning and at the top of the projectiles motion. Use one vector arrow to represent the direction of the at the beginning and at the top of the projectiles motion. Do the same thing for velocity and acceleration.
We can see that the force is caused by gravity and faces the center of the Earth the entire trip. Since the acceleration is caused by this force, the acceleration vector is in the same direction as the force vector. Position is determined by the resultant velocity so those arrows will mirror each other as well.
This completes this comprehensive review for the semester one final exam. Thank you for taking the time to review with me. If you have studied hard you deserve to do well. Good luck and have a nice day.
