Wheels Flashcards
Wagon-less Wagon experiencing 3 forces?
1) It’s downward weight
2) Support force from surface
3) Horizontal frictional forces from surface (violates N’s1st law?)
Friction?
Forces exerted by surfaces on each other.
- Adheres N’s 3rd Law (all forces)
- Acts parallel (along) surfaces
Frictional Forces oppose____?
relative motion b/w two surfaces in contact
- exerted parallel to the surfaces
Relative Motion
Motion against velocity’s directio
Surfaces in contact produce friction that has the same____?
Velocity, objects move together vs sliding across each other
Frictional Forces are____ external forces on objects
Opposite
Hold can w/ 2 fingers, exerting any frictional forces on can? In what direction forces?
Yes, exerting upward frictional force on can (your relative motion opposed by cans’ downward weight)
& .•. support cans’ weight
Surfaces at rest & in contact ____ into____ _____ & are .•. particularly _____ to the ____ of ______.
- Each other
2. Resistant to the start of sliding
Friction depends (3)
- type of surface
- pressure of surfaces against each other
- whether/not surfaces actively sliding across
Frictional Forces dependant on?
Support forces,
a bigger support force b/w 2 surfaces = bigger frictional forces
of contact points proportional____
of support forces
Contact points responsible for?
Frictional forces
Amontons 1st law of friction?
Frictional forces b/w 2 surfaces are proportional to support forces b/w them.
Amontons 2nd Law Friction
Frictional Forces b/w 2 surfaces don’t depend their apparent contact area.
- Surface you see touching floor not really (all) surface touching floor.
For any two surfaces,
coefficient of friction = ?
frictional force (forces available when try sliding them/ support force (b/w 2 surfaces)
- typically 0.5, 0.3 etc.
Frictional forces b/w tire & surface allow you to (3)?
1) speed up
2) slow down
3) turn
- w/out frictional you’d be inertialo
Want tires that (2)
1) grip road well (higher coefficient of friction)
2) wheels tightly pressed against road producing higher support force b/w road & tire.
Static Friction
Surfaces touching & not sliding across each other.
- forces causing surfaces not move (experience 0 net force & 0 acceleration
Sliding Friction
Objects coasting across each other.
The harder press 2 surfaces together___ the higher/lower (?) ___ ____ _____ can obtain
Higher peak static friction it can obtain
Static friction is ____ & there’s a ____ of static friction before moving.
Adjustable & there’s a limit of static friction before moving.
When gives up/at its limit frictional force turns into?
Sliding Friction
When sliding box across floor need higher/lower force to start moving vs force keep box coasting?
Need higher force when first move box vs lower force needed keep coasting
Coulomb’s 3rd Law of Friction
Sliding frictional forces are independent of sliding speed.
- faster you push/pull doesn’t affect force applied
Sliding friction always in direction that____ ____ _____ to _____
Direction that opposes relative motion to surfaces.
Static friction or Sliding friction higher force & better grip?
Static friction.
- mountain peaks grip together & settle in to make higher friction
vs
- mountain peaks sliding across each other.
Is sliding friction adjustable & what does it depend on?
It’s not adjustable & it depends on how hard surfaces press each other (obey coulombs 3rd law friction)
Sliding Friction wastes
Energy.
(For moving box) sliding friction converts box’s ____ energy into ____ energy.
Kinetic energy into thermal energy.
When box slides to stop on motionless floor, who does work on other?
Floor does negative work on box (pushes box opposite direction its velocity) &
Box does 0 work on motionless floor even though pushing on it.
