Describing the System [1] Flashcards
(40 cards)
what is the law of inertia?
a body stays in its state of rest OR in motion, unless it is compelled to change that state by forces impressed upon it
- a body in motion stays in motion ect..
What is the law of acceleration?
change in motion is directly proportional to the magnitude of the applied force
F = MA
What is acceleration?
Observed change in motion
- even deceleration falls under this category
What is the law of action-reaction?
To every action there is always an opposed and equal reaction
- these forces occur in pairs
(Think of a race car; gravity pulls down, road pushes up; & engine propels forwards, drag/friction pulls backwards)
What are JRF’s?
Joint Reaction Forces: they keep our joints stable while our muscles move
- ex: shoulder abduction; humeral head stays in socket while deltoid muscles move
What is considered a force?
Something with the capability to cause a change in motion of a system
- ex: push or pull
What are the different properties of a force?
- magnitude: size of applied force
- orientation: alignmnet of the vector in relation to cardinal directions
- direction: the way the force is applied
- line of action: imaginary line extending indefinitely along the vector through tip and tail
- point of application: point at which the system receives the applied force
What types of forces are there?
- Non-contact (field) forces
- Contact forces
- External and Internal forces
- Action and reaction forces
Explain non-contact (field) forces
Law of universal gravitation explains the ineraction of objects even when not in contact with each other
- ex: magnets
- field: any object possessing mass creates an invisible field of influence stretching throughout the space
What type of force is the electromagnetic force?
Non-contact field force
This force it is between electric charges
- gravitational forces exists between bodies of mass
- our body expeireces both electromagnetic and gravitational forces
What are contact forces?
the result of phsyical contact between 2 bodies
ex: hitting a ball with a bat
What are external forces?
those that intercat with the system from the outside
- change the motion of the system
What are internal forces?
they act within the defined system
- they change the shape of the system
What is an action force?
The initially applied force
What is a reaction force?
the simultaneous equal counterforce acting in the opposite direction to the action force
- locomotion
How does Newton’s 3rd law relate to action & reaction forces?
Essentially the force the body places on the earth, earth places back on the body
- intenal forces on the system are the muscles
- the exertrnal forces are the equal and opposite force applied by the earth; which creates motion
What is ground reaction force?
keeps us stable as we walk
- on sand GRF is not quite the same and can’t give us back the force we put on it
How does gravity work in relation to weight?
Gravity pulls on an objects mass with a ceratin amount of force (it gives us weight in a downward direction)
- Weight: the measure of the force with which gravity pulls upon an objects mass
-
weight changes as we get closer to and darther from the center of the ea
What are the 2 types of resultant forces?
- Centripetal force: any force that causes a system to exhibit circular motion (center seeking)
- Centrifugal force: the force that is equal to and opposite the centripetal force (center fleeing/fugitive)
What is friction?
A force that resists the sliding of 2 objects in contact
- exists when 2 objects in contact have the potential to slide across each other
- vectors that represent frinction force has a direction that is opposite of the potential sliding direction and parallel to the 2 surafces in contact
friction is resistance to sliding
What is static friction?
occurs when 2 contacting surfaces are not sliding/moving relative to each other BUT do posses the potential for movement
- to move a box the static friction < applied force
- thus once it moves it goes from static friction to kinectic friction
desk has static friction against the floot
What is kinetic friction?
friction in which 2 surfaces are already sliding relative to each other
- easier to move a box with kinetic frinction than static friction bc coefficient is lower
What is rolling friction?
occurs whenever one surface is rolling over another but not sliding
- coefficient of rolling friction is < than static and kinetic which is why this is the easiest to do
How does pressure interact with force?
Pressure is the magnitude of applied force acting over a certain area
- Pressure = Force/Area
Ex: laying on a bed of nails manipulates pressure to avoid puncture
- weight of a person = applied force (F)
- area over which it is applied = total area of the tips of the nails (A)
