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Motion and Stability: Forces and Interactions (Forces and Motion (By the…
Motion and Stability: Forces and Interactions
Forces and Motion
By the end of 2nd grade: push and pull
different strengths/directions
sliding; friction
collision/connection
By the end of 5th grade: force has strength and direction
object at rest = multiple forces with net force zero
patterns of motion can allow us to predict future motion
By the end of 8th grade: Newton's 3rd law
greater the mass, greater the force to change motion
forces can change an object's shape/orientation
By the end of 12th grade: Newton's 2nd law & momentum
2nd law predicts changes in motion of macroscopic objects but not subatomic scales or momentum
momentum = mass x velocity
momentum is always conserved
Newton's Laws
2nd Law: Force = mass x acceleration
3rd Law: the force exerted by the first object on the second is equal to the force that the second objects exerts on the first, but in the opposite direction
An understanding of the forces between objects is important for describing how their motions change, as well as for predicting stability or instability in systems at any scale.
Motion
: if the forces on an object is not zero, motion will change
Sometimes
shape
or
orientation
can also change.
Static
: multiple forces on an object sum up to zero
Types of Interactions
Gravity
Objects with mass are a source of gravity and are affected by all other objects with mass.
Newton's law of universal gravitation provides the math model to describe and predict effects of gravity between two objects.
Electromagnetism
Forces can be attractive or repulsive
Coulomb's law provides the mathematical model to describe and predict the effects of electrostatic forces.
Strong and Weak Nuclear Interactions
Inside atomic nuclei; determine nuclear sizes, stability, and rates of radioactive decay
Don't need to be in contact; forces can transfer energy through space.
By the end of 2nd grade: when objects touch/collide, they push on one another and can change motion/shape
By the end of 5th grade
Objects in contact exert forces on each other
Objects don't need to be in contact to exert forces on each other.
Gravity on Earth pulls objects towards the center of the Earth.
By the end of 8th grade
Electric/magnetic forces can be attractive or repulsive
Gravitational forces are always attractive
Large-scale gravitation governs the evolution and maintenance of objects in space
By the end of 12th grade
Newton's Universal Law of Gravitation
Coulomb's law
Forces at a distance are explained by fields permeating space
Stability and Instability in Physical Settings
Stability/instability depends on the balance of competing effects.
Stable System
: the internal and external forces are such that any small change results in forces that return the system to it's prior state.
It is not easy to predict about a system's future when it has a lot of components.
By the end of 2nd grade: an object staying at rest or moving depends on multiple pushes and pulls
By the end of 5th grade
A system can change as it moves one direction, shifts back and forth, or goes through cyclical patterns.
Changes can happen quickly or slowly
By the end of 8th grade
A stable system
A system can be static but unstable
A system can be changing but have a stable repeating cycle of changes
Many systems rely on feedback mechanisms to maintain stability
By the end of 12th grade
Systems often change in predictable ways
When a system has a lot of component pieces, it makes it hard to predict about the system.