Shared Flashcard Set

Details

Motion and Force
N/A
48
Physics
Not Applicable
10/20/2012

Term
 FRICTION
Definition
 Opposite force that acts on something being pushed. It's stronger on a rough surface so the force you exert needs to be stronger to overcome it
Term
 Newton's first law of motion
Definition
 Objects stay at rest or remain in uniform motion unless acted on by a force
Term
 AN OBJECT MOVING AT CONSTANT VELOCITY
Definition
 Is acted on by no forces or the forces acting on it are balanced (resultant = 0)
Term
 INVESTIGATING FORCE AND MOTION
Definition
 Trolley and motion sensor connected to computer. Computer processes signals from motion sensor and displays graph showing how velocity varies with time
Term
 IF THE TROLLEY IS PULLED AT CONSTANT FORCE
Definition
 Velocity time graph will show that velocity increases at constant rate.
Term
 FORCE
Definition
 Proportional to ma    F = ma    AKA Newton's second law
Term
 WEIGHT
Definition
 Weight is force    W = ma   a = g (acceleration of free fall)    W = mg
Term
 EQUILIBRIUM
Definition
 An object in equilibrium support force  equal and opposite to weight.
Term
 INERTIA
Definition
 Mass of object. It's resistance to change of motion.   bigger force to move an object with a certain acceleration   Less force to move object with same accerlation but less mass
Term
 TWO FORCES IN THE OPPOSITE DIRECTION
Definition
 When two forces act on an object in opposite directions, the object accelerates in the direction of the larger force
Term
 RESULTANT FORCE OF OBJECTS ACTED ON FORCES IN OPPO DIRECTIONS
Definition
 Resultant force = F1 - F2 = ma   At this point support  = weight
Term
 TRAILERS
Definition
Term
 ROCKETS
Definition
Term
 LIFTS
Definition
Term
 PULLEY
Definition
Term
 SLIDING DOWN A SLOPE
Definition
Term
 DRAG FORCE
Definition
 Depends on: shape of object, speed and vicosity of fluid it's travelling through     greater speed = bigger drag force
Term
 MOTION OF AN OBJECT FALLING IN FLUID
Definition
 Speed increases as object released from rest. This means drag force increases.      Resultant force = difference between weight and drag.  As drag increases, acceleration decreases until reaches terminal velocity. When drag = weight acceleartion = 0 so constant speed
Term
 ACCELERATION AT ANY INSTANT
Definition
Term
 F = mg - D
Definition
 force = mg - drag    acceleration = g - D / m
Term
 INITIAL ACCELERATION
Definition
 Is 9.81 (g) because speed is zero. so drag is zero the moment it's released
Term
 AT TERMINAL SPEED
Definition
 Potential energy lost by object is converted to internal energy of fluid by drag force
Term
 MOTION OF A POWERED VEHICLE
Definition
 depends on engine power (motive power) vehicle with streamlined shape can reach higher top speed that vehicle with same motive power that isn't streamlined
Term
 ACCELERATION OF A POWERED VEHICLE
Definition
 Engine force(motive) - resistive force/ mass   a = FE - FR / m
Term
 THINKING DISTANCE
Definition
 Distance travelled in time it takes driver to react    S1 = speed x reaction time    reaction time effected by drugs, alcohol and mobile phones
Term
 BRAKING DISTANCE
Definition
 Distance in time taken to stop safely from when brakes are first applied. Assuming constant deceleration to zero from v:   S2 = v2/2a
Term
 STOPPING DISTANCE
Definition
 Thinking distance  + braking distance   = vt0 + v2 / 2a   v = speed before brakes were applied
Term
 STOPPING DISTANCES HIGHWAY CODE
Definition
 30mph = 30ft Thinking , 45ft braking   50mph = 50ft thinking, 125ft braking   70mph = 70ft thinking, 245ft braking
Term
 HOW DOES A CAR MOVE FORWARD
Definition
 By pushing backwards on the road
Term
 HOW DOES FRICTION PREVENT SKIDDING
Definition
 friction between tyres and road prevent wheel spinning.   if driver accelerates too fast, wheels skid beacuse there is a limit to friction between tyres and road   wheels are slowed down by brakes if they don't skid   increase braking force increases friction force
Term
 UPPER LIMIT OF FRICTION (LIMITING FRICTION)
Definition
 If this is reached, between tyres and road, wheels skid. Brakes lock and vehicle moves uncontrollably. Most vehicles have anti-lock brake system that has a speed sensor on each wheel that controls hydraulic valves in brake so brake pressure is reduced on wheel to stop it locking
Term
 TESTING FRICTION
Definition
 Pull on block until it slides limiting frictional force = pull force on block
Term
Definition
 Skidding is more likely. Limiting friction is reduced. To stop vehicle safely brakes must be applied with less force to avoid skidding. Driver must ensure bigger gap to car in front to slow down safely
Term
 CONDITIONS OF TYRES
Definition
 Tread must not be less than a certain depth. UK legal 1.6mm at 3/4 of the tyre. If pressure is too great or small, or uneven, tyre will wear out unevenly and become unsafe
Term
 HOW MUCH ACCELERATION/DECELERATION CAN A PERSON WITHSTAND?
Definition
 20g for a few miliseconds with severe injury 5g causes injury
Term
 IMPACT FORCE
Definition
 Acceleration = 30mg-2  Acceleration = 3g    Impact force = 3mg so impact is 3g even though this statement is wrong
Term
 CONTACT  TIME WITH COLLISIONS
Definition
 When objects collide and bounce off each other they are in contact for a certian time. Shorter contact time, greater impact force for same initial velocities of both objects
Term
 CONTACT TIME WITH COLLISIONS THAT REMAIN STUCK TOGETHER
Definition
 If are stuck together, they exert forces on each other until they are moving at the same velocity. Duration of impact force isn't the same as contact time in this situation
Term
 IMPACT TIME
Definition
 Calculated using s = 1/2(u+v)t where s is the distance moved by that vehicle during impact.
Term
 KINETIC ENERGY AND IMPACT FORCE
Definition
 F = change of kinetic energy / impact distance
Term
 CAR SAFETY
Definition
 Impact force reduced when impact time increases
Term
 VEHICLE BUMPERS
Definition
 Give way a little in low speed impacts so increase impact time
Term
 CRUMPLE ZONE
Definition
 Engine compartment dives way in front impact. Impact time increases, so force decreases
Term
 SEAT BELTS
Definition
 Restrains wearer from crashing into vehicl frame in a fron impact. Restraining force is much less than impact force. Wearer is stopped more gradually with seatbelt than without
Term
 COLLAPSIBLE STEERING WHEEL
Definition
 Impact force reduced if driver hits the wheel as impact time is increased
Term
 AIRBAGS
Definition
 Acts as cushion  increases impact time  Impact force spread over contact area with seat belt, so pressure is less on body
Supporting users have an ad free experience!