UNIT 2: Dynamics
This unit deals with the motion of the object and how it is changed by the 'force'. Different types of forces can be responsible for a certain motion and they are important for understanding everyday things.
This unit deals with the motion of the object and how it is changed by the 'force'. Different types of forces can be responsible for a certain motion and they are important for understanding everyday things.
1. Newton’s First Law (Law of Inertia)
Inertia
An object's resistance to change in motion which is solely dependent on the mass an object has
more mass --> more inertia
Newton's First Law of Inertia
An object will continue to move at a constant velocity unless it feels an unbalanced push or pull
--> An object at rest will remain at rest and an object in motion will maintain a constant velocity unless acted upon by a net external force.
Inertia
An object's resistance to change in motion which is solely dependent on the mass an object has
more mass --> more inertia
Newton's First Law of Inertia
An object will continue to move at a constant velocity unless it feels an unbalanced push or pull
--> An object at rest will remain at rest and an object in motion will maintain a constant velocity unless acted upon by a net external force.
no external force acting on the object
net force = normal force + gravitational force = 0
net force = normal force + gravitational force = 0
2. Newton’s Second law
Law of Acceleration, Net Force, and Mass
Acceleration is proportional to the net (total) force acting on a system, and inversely related to the total moss of a system
more mass --> more inertia --> less acceleration
more force --> more acceleration
Law of Acceleration, Net Force, and Mass
Acceleration is proportional to the net (total) force acting on a system, and inversely related to the total moss of a system
more mass --> more inertia --> less acceleration
more force --> more acceleration
3. Newton's Third Law
For every action there is an equal and opposite reaction
--> Forces always occur in pairs and are equal in strength and opposite in direction
For every action there is an equal and opposite reaction
--> Forces always occur in pairs and are equal in strength and opposite in direction
When a person pushes a wall, a wall pushes back equally
4. Identifying interactions: System Schemas and Force Diagrams
System Schema
A visual way to keep track of the objects in a system and how they interact
FORCES = INTERACTION BETWEEN TWO OBJECTS
System Schema
A visual way to keep track of the objects in a system and how they interact
FORCES = INTERACTION BETWEEN TWO OBJECTS
- Each object is a circle
- Every force is a line connecting two circles
- Every force is a line connecting two circles
Free Body Diagrams (FBD)
We use a force diagram to show direction (and magnitude)
STEPS
- Taking one object of interest and making it a dot
- Drawing an arrow for each force acting on object from the dot in the direction the force acts on the object
- Labeling the force with type of force, other interacting object, and object of interest
We use a force diagram to show direction (and magnitude)
STEPS
- Taking one object of interest and making it a dot
- Drawing an arrow for each force acting on object from the dot in the direction the force acts on the object
- Labeling the force with type of force, other interacting object, and object of interest
System Schema
Force Diagram
object of interest = you
object of interest = you
5. Force Calculations
Fnet = ma = Fapplied - Ffriction
If there is no friction, then Fnet = Fapplied
If there is a friction and surface is horizontal surface, Ff = umg, where u = coefficient of friction.
Value of u is different from surface to surface.
And even if it is the same surface, coefficient of static friction and coefficient of kinetic friction are also different.
Fnet = ma = Fapplied - Ffriction
If there is no friction, then Fnet = Fapplied
If there is a friction and surface is horizontal surface, Ff = umg, where u = coefficient of friction.
Value of u is different from surface to surface.
And even if it is the same surface, coefficient of static friction and coefficient of kinetic friction are also different.
6. Solving Problems with Forces and Motion
steps
- gather information
- use information
- repeat
steps
- gather information
- use information
- repeat
System Schema
Force Diagram
If net force is zero, object may be at rest or move with constant velocity. Assuming the wagon is traveling with constant velocity of
Therefore, given that F applied = 100 N, F friction must also be 100 N
Fx net = Fapplied - Ffriction = 100 - 100 = 0N
Fn - Fg = 0 N
Therefore Net force is 0 N.
Therefore, given that F applied = 100 N, F friction must also be 100 N
Fx net = Fapplied - Ffriction = 100 - 100 = 0N
Fn - Fg = 0 N
Therefore Net force is 0 N.
7. Relating Representations of Motion and Force Models
1) For the first two d vs t and v vs t graph, we can conclude that object moves with a constant
Therefore, object's acceleration must be 0, and object has a net force of 0 N
2) For the first two d vs t and v vs t graph , we can conclude that object moves with a constant acceleration. Therefore, object has a constant net force such that Fnet = ma
Therefore, object's acceleration must be 0, and object has a net force of 0 N
2) For the first two d vs t and v vs t graph , we can conclude that object moves with a constant acceleration. Therefore, object has a constant net force such that Fnet = ma
8. Solving Problems with Forces and Motion
F net = F applied - F friction
F applied is given as 10 N, and F friction may be calculated as Ff = umg = 0.2 x 10 kg x 9.8 m/s^2 = 19.6 N
F net = 100 - 19.6 = 80.4 N to the right
F net = ma => a = 80.4 N / 10 kg = object is moving with acceleration of 8.04 m/s^s to the right
F applied is given as 10 N, and F friction may be calculated as Ff = umg = 0.2 x 10 kg x 9.8 m/s^2 = 19.6 N
F net = 100 - 19.6 = 80.4 N to the right
F net = ma => a = 80.4 N / 10 kg = object is moving with acceleration of 8.04 m/s^s to the right
9. Citations
Stickmanphysics.com. Accessed November 15, 2021. https://stickmanphysics.com/stickman-physics-home/forces/newtons-third-law-of-motion-action-reaction-pairs/.
Myrank. “Newton's Second Law of Motion.” MyRank, November 3, 2017. https://blog.myrank.co.in/newtons-second-law-of-motion/.
Work. Accessed November 15, 2021. http://labman.phys.utk.edu/phys135core/modules/m6/work.html.
Stickmanphysics.com. Accessed November 15, 2021. https://stickmanphysics.com/stickman-physics-home/forces/newtons-third-law-of-motion-action-reaction-pairs/.
Myrank. “Newton's Second Law of Motion.” MyRank, November 3, 2017. https://blog.myrank.co.in/newtons-second-law-of-motion/.
Work. Accessed November 15, 2021. http://labman.phys.utk.edu/phys135core/modules/m6/work.html.