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THE MCAT-PHYSICS 2
FORCES
| Question | Answer |
|---|---|
| The force of air resistance is ALWAYS constant for any mass. T/F | TRUE |
| What changes force of air resistance? | speed, SA, shape |
| What does mass change with AR then? | changes effect of air resistance (path) but doesn't change air resistance F=ma and bowling pins |
| Why does a large mass and small mass fall at the same rate? | Larger inertia associated with larger mass means a larger force required to change its motion at the same rate |
| Universal gravitation: What do two objects experience? | Experience same gravitational force but acceleration is different |
| What is weight? | measure of gravitational force on a body |
| rotational inertia? | measure of an object's resistance to changes to its rotation |
| What is center of mass? | single point where a single force can be applied in any direction causing all points in system to accelerate equally |
| Inclined plane: When frictionless, what forces act? | gravity and normal force |
| What do machines do? | reduce amount of force needed to accomplish a task |
| What don't machines do? | reduce amount of work that needs to be done |
| Mechanical advantage equation? | weight of object to be supported / applied force needed to support object |
| What do you need to overcome when push object up inclined plane? | Overcome both parallel component of gravity and friction |
| Inclined plane: nonmoving object | parallel vector of gravity = static friction |
| Inclined plane: object going down @ constant velocity | parallel vector of gravity = kinetic friction |
| Inclined plane: object accelerating down inclined plane | parallel vector of gravity > Fk |
| Inclined plane: object begins to slip on inclined plane | parallel vector of gravity > Fs |
| What are the forces acting on a block on inclined plane? | gravity and normal force |
| centripetal acceleration | -speed never changes but object is always accelerating -points toward center of circle |
| centripetal force | -points toward center of circle -acceleration is ALWAYS accompanied by a force -Fc is created by gravitational force |
| What are the ONLY 3 forces? | -gravitational, electromagnetic, contact -these forces create and cause all other forces |
| Stuff moving in a circle? Think --> | F = mv^2 / r |
| Kepler's Laws | 1.) All orbital paths elliptical 2.) orbiting object moves faster and subject to greater force when closer to object it orbits 3.) T^2 is proportional to R^3 |
| What is apparent weight often associated with? | normal force |
| Elevator accelerating up = Elevator decelerating down = | -elevator decelerating down -elevator decelerating up |
| what forces act on uniform circular motion? | centripetal force (centripetal "a" ) directed towards center of circle |
| What forces act on nonuniform circular motion? | tangential force to change "a" and centripetal force produce resultant force and "a" NOT directed towards center of circle |
| Contact situations always have what forces? | Fn perpendicular and frictional parallel |
| Is static friction constant? | NO --> can reach a threshold point |
| Is kinetic friction constant? | Yes! once it moves it moves |
| Which is greater, u(s) or u(k) friction? | u(s) |
| Can static friction accelerate an object from rest? | YES |
| What does frictional force oppose? | -applied force -no applied force - frictional force does all of the work |
| Why (-) in Hooke's Law? | force is opposite direction to displacement |
| translational equilibrium | constant speed (0 or nonzero) and constant direction |
| rotational equilibrium | not rotating or constant rotation |
| static equilibrium | velocity is constant 0 |
| dynamic equilibrium | velocity is constant and not zero |
| What does a non-equilibrium state mean? | There is acceleration! |
| How to change angular velocity? | Apply torque |
| What are some examples of external forces? | friction, air resistance, normal, applied force |
| How does external force affect total ME? | -External forces are nonconservative forces -change the total ME depending on whether positive or negative work |
| What are examples of internal forces? | gravity, magnetic, electrical, spring force |
| How does internal forces affect total ME? | -Internal forces are conservative forces -do not change the total ME -type of energy form changes |
| What is work done for external forces equal to? | change in mechanical energy |
| Is work the same as energy? | NO --> work is when a quantity of energy is moved from one system to another |
| What remains constant for conservative forces? | sum of kinetic and potential energies |
| Law of Universal Gravitation Equation | F = Gm1m2 / r^2 |
| Kinetic Friction equation | Fk = uk * Fn |
| Static Friction equation | Fs = us * Fn |
| What is static friction? | friction opposing motion when a stationary object and surface are not moving |
| What is kinetic friction? | force resisting motion once stationary object and surface are moving |
| When is coeff of friction max? | when 2 surfaces are not moving |
| Once a block starts to slide, is there acceleration? | YES |
| Mutual forces exerted during collisions are equal / unequal in magnitude? | equal |
| What does friction depend on? | coefficient of friction, angle, and normal force |
| As angle increases for a box on an inclined plane, ____ decreases which causes net accelerating force acting on box. | normal force |
| As soon as equilibrium is disrupted, there is _____. | acceleration |
| What happens to the peak height when you kick an object into air with air resistance? | reaches lower peak, takes longer to reach ground than peak |
| What does backspin create and what to do to compensate? | additional flight time --> decrease launch angle |
| What does topspin create and what to do to compensate? | reduces flight time --> increase launch angle |
| Can friction cause acceleration? | YES |
| Does friction do work on an object? | YES --> drains energy |
| Considering air resistance, why does an elephant fall faster than a feather? | -elephant never reaches terminal velocity --> accelerates constantly -feather quickly reaches terminal velocity |
| Considering no air resistance, does an elephant or feather fall faster? | fall the same |
| Does the force of AR ever change for a mass? | NO |
| What does AR take away from an object? | takes away energy |
| Why does large SA increase AR? | more collisions with air molecules |
| HIgher the velocity, higher /lower AR? | greater the AR |
| Why do larger masses experience less deceleration due to AR? | F= m*a -force constant, mass increases, a decreases |
| In a collision, two objects hit each other with? | equal force |
| Does mass change if gravity changes between two planets? | NO --> only weight changes |
| With an elevator, is the tension of the cable line ever zero? | NO |
| Moving in from a larger circle to a smaller circle, does tangential speed increase or decrease? | decrease |
| 2 important rotational motion equations? | -a = v^2 / r (tangential speed) -w = v/r (angular velocity) |
| Does a planet's orbit depends on the planet's mass? | NO |
| Does an orbiting object move faster or slower when orbital radius decreases? | faster |
| Higher coefficient of friction means? | greater friction |
| Can static friction accelerate object from rest? | YES |
| Why is it harder to start walking on an icy floor than a carpeted floor? | us for ice is much lower than us for carpet |
| Is acceleration on an inclined plane parallel / perpendicular to surface of plane? | PARALLEL |
| Mechanical advantage | weight of object to be supported / actual applied force to support object |
| What is the mechanical advantage of an inclined plane? | 1 / sin theta |
| How does the tension change within a rope in a pulley system? | IT DOESN'T CHANGE --> CONSTANT THROUGHOUT |
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