Reflection 1
After finishing this chapter, i have learnt that to understand the concepts is more necessary than to practice a lot. Since most of the questions can be solved by using several formulas, to understand every formula and use them properly becomes the most important task for me. So i believe understanding all the formula and the concepts is the key to do well on physics. (Hanwen Xing)
Comment by Edmund: I agree. Understanding is the key.
Comment by Stanley: Formula is the base.
Comment by Edmund: I agree. Understanding is the key.
Comment by Stanley: Formula is the base.
Reflection 2
In this dynamics unit, I explored the concepts of the Newton laws and various other concepts such as the pulley problems, the incline problems and reviewed problems such as Free Body Diagram and Elevator problems. The Newton's Three Laws: Inertia, Fnet=ma, and action-reaction forces are the basic concepts of dynamics. The other problems mentioned before are applications of these laws(pulley, elevator, etc.) and ways to solve problems.(FBD).
I experienced difficulties on incline problems because it has two dimensions, which add to the difficulty level. Because it has two dimensions, I have to calculate both the x-axis and y-axis forces, using the vector. Therefore, I always encounter difficulty when trying to analyze the problem clearly.
For all dynamics problems, the first step is to analyze the problem. To analyze, I just draw the FBD first and analyze forces on each dimension. After finding out the forces, I try to find the unbalanced force that creates the net force. If it has two dimensions, vector concepts have to be applied. Therefore, I can calculate the net force and other required data. After that, the answer can be got by applying formula. (Edmund Zhai)
Comment by Hanwen Xing: The way to apply the formula is more important than to memorize it.
Comment by Stanley: Practice more questions with different styles will help you further?
I experienced difficulties on incline problems because it has two dimensions, which add to the difficulty level. Because it has two dimensions, I have to calculate both the x-axis and y-axis forces, using the vector. Therefore, I always encounter difficulty when trying to analyze the problem clearly.
For all dynamics problems, the first step is to analyze the problem. To analyze, I just draw the FBD first and analyze forces on each dimension. After finding out the forces, I try to find the unbalanced force that creates the net force. If it has two dimensions, vector concepts have to be applied. Therefore, I can calculate the net force and other required data. After that, the answer can be got by applying formula. (Edmund Zhai)
Comment by Hanwen Xing: The way to apply the formula is more important than to memorize it.
Comment by Stanley: Practice more questions with different styles will help you further?
Reflection 3
After the examination of Dynamics, I find my weak points on the lesson. For these, I plan to understand further in formulas, also, practice more questions will improve my skills as well. Draw the Free Body Diagrams for the questions will assist me to understand the concepts of Newton's Second Law. Another way, questions with different styles will help me to adapt any kinds of exams.
Comment by Edmund: Yes, drawing FBD is essential to understand the concepts.
Comment by Hanwen Xing: Totally agree, FBD is definitely the ultimate weapon to all problems
Comment by Edmund: Yes, drawing FBD is essential to understand the concepts.
Comment by Hanwen Xing: Totally agree, FBD is definitely the ultimate weapon to all problems
Project-----PLANE
The main concepts of dynamics are present in the flight and landings of planes. Planes experience different forces such as the thrust, lift, gravity and air resistance in their flights. In the following sections, we will explore the dynamics concepts and its application of planes.
Basic Concepts of Dynamics
Basic Laws: Newton's Three Laws
Newton's First Law: An object at rest stays at rest and an object in motion moves with constant velocity unless acted upon by a net external force.
Newton's Second Law: Fnet=ma. When an unbalanced force acts on an object, it accelerates the object in the same direction of force.
Newton's Third Law: Forces occur in pairs. F AB = - F BA
Free Body Diagram: FBD is used to solve almost all force-related questions. The diagram gives a detailed overview of the problem with all forces labelled on the box representing the object.
The diagram below is a sample a FBD
Newton's First Law: An object at rest stays at rest and an object in motion moves with constant velocity unless acted upon by a net external force.
Newton's Second Law: Fnet=ma. When an unbalanced force acts on an object, it accelerates the object in the same direction of force.
Newton's Third Law: Forces occur in pairs. F AB = - F BA
Free Body Diagram: FBD is used to solve almost all force-related questions. The diagram gives a detailed overview of the problem with all forces labelled on the box representing the object.
The diagram below is a sample a FBD
Dynamics Application of Planes
The concepts of dynamics are applied in the motion of plane flights.
1) Take-off Process
1) Take-off Process
- Thrust: The force generated by the engine that pushes the airplane forward
- Gravity: W=mg, force dragging down the airplane, balancing the normal force
- Friction: Ff=µFn, force against the thrust force on the runway.
- Lift: When the plane leaves the runway, the y-axis force is unbalanced and the lift force makes the plane ascend.
2) Landing Process
- Gravity: W=mg, force dragging down the airplane.
- Friction: Friction force applied by air(air resistance) and runway
- Lift: When the plane is landing, this force prevent the plane from doing free falling.
Real Life Example
The Boeing 787 has the mass of 165,108kg. One day the plane is cruising at 700km/h, and going to land. After it lands, the horizontal velocity becomes 500km/h. If the air resistance is constant (3000N) and the ground's coefficient of kinetic friction is 0.4. What is the total time it costs from land to completely stop?
Fnet=ma (the basic formula of dynamic problems)
Ff-air+Ff-land=ma (Fnet is the sum of firction of air and land)
3000+μmg=ma (plug in numbers)
a=(3000N+0.4x165108kgx9.8m/s^2)/165108kg (Calculation)
a=3.94m/s^2
V=at (the formula for acceleration problems)
t=V/a=[(500/3.6)m/s]/(3.94m/s^2) (Plug in numbers)
t=35.25s
therefore, the time for landing is 35.25s.
Fnet=ma (the basic formula of dynamic problems)
Ff-air+Ff-land=ma (Fnet is the sum of firction of air and land)
3000+μmg=ma (plug in numbers)
a=(3000N+0.4x165108kgx9.8m/s^2)/165108kg (Calculation)
a=3.94m/s^2
V=at (the formula for acceleration problems)
t=V/a=[(500/3.6)m/s]/(3.94m/s^2) (Plug in numbers)
t=35.25s
therefore, the time for landing is 35.25s.