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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 |
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Term
Newton's first law of motion |
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Definition
| Objects stay at rest or remain in uniform motion unless acted on by a force |
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AN OBJECT MOVING AT CONSTANT VELOCITY |
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Definition
| Is acted on by no forces or the forces acting on it are balanced (resultant = 0) |
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INVESTIGATING FORCE AND MOTION
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Definition
| Trolley and motion sensor connected to computer. Computer processes signals from motion sensor and displays graph showing how velocity varies with time |
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Term
IF THE TROLLEY IS PULLED AT CONSTANT FORCE |
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Definition
| Velocity time graph will show that velocity increases at constant rate. |
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Term
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Definition
Proportional to ma
F = ma
AKA Newton's second law |
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Term
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Definition
Weight is force
W = ma
a = g (acceleration of free fall)
W = mg |
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Term
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Definition
| An object in equilibrium support force equal and opposite to weight. |
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Term
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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 |
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Term
TWO FORCES IN THE OPPOSITE DIRECTION |
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Definition
| When two forces act on an object in opposite directions, the object accelerates in the direction of the larger force |
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Term
RESULTANT FORCE OF OBJECTS ACTED ON FORCES IN OPPO DIRECTIONS |
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Definition
Resultant force = F1 - F2 = ma
At this point support = weight |
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Definition
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Definition
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Definition
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Definition
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Definition
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Term
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Definition
Depends on: shape of object, speed and vicosity of fluid it's travelling through
greater speed = bigger drag force |
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Term
MOTION OF AN OBJECT FALLING IN FLUID
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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 |
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Term
ACCELERATION AT ANY INSTANT |
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Definition
| gradient of speed time curve |
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Term
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Definition
force = mg - drag
acceleration = g - D / m |
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Term
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Definition
| Is 9.81 (g) because speed is zero. so drag is zero the moment it's released |
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Term
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Definition
| Potential energy lost by object is converted to internal energy of fluid by drag force |
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Term
MOTION OF A POWERED VEHICLE |
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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 |
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Term
ACCELERATION OF A POWERED VEHICLE |
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Definition
Engine force(motive) - resistive force/ mass
a = FE - FR / m |
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Term
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Definition
Distance travelled in time it takes driver to react
S1 = speed x reaction time
reaction time effected by drugs, alcohol and mobile phones |
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Term
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Definition
Distance in time taken to stop safely from when brakes are first applied. Assuming constant deceleration to zero from v:
S2 = v2/2a |
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Term
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Definition
Thinking distance + braking distance
= vt0 + v2 / 2a
v = speed before brakes were applied |
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Term
STOPPING DISTANCES HIGHWAY CODE |
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Definition
30mph = 30ft Thinking , 45ft braking
50mph = 50ft thinking, 125ft braking
70mph = 70ft thinking, 245ft braking |
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Term
HOW DOES A CAR MOVE FORWARD |
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Definition
| By pushing backwards on the road |
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Term
HOW DOES FRICTION PREVENT SKIDDING |
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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 |
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Term
UPPER LIMIT OF FRICTION (LIMITING FRICTION) |
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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 |
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Term
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Definition
Pull on block until it slides
limiting frictional force = pull force on block |
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Term
BRAKING DISTANCE ON ICY ROAD |
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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 |
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Term
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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 |
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Term
HOW MUCH ACCELERATION/DECELERATION CAN A PERSON WITHSTAND? |
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Definition
20g for a few miliseconds with severe injury
5g causes injury
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Term
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Definition
Acceleration = 30mg-2
Acceleration = 3g
Impact force = 3mg so impact is 3g even though this statement is wrong
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Term
CONTACT TIME WITH COLLISIONS |
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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
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Term
CONTACT TIME WITH COLLISIONS THAT REMAIN STUCK TOGETHER |
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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 |
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Term
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Definition
Calculated using s = 1/2(u+v)t where s is the distance moved by that vehicle during impact.
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Term
KINETIC ENERGY AND IMPACT FORCE |
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Definition
| F = change of kinetic energy / impact distance |
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Term
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Definition
| Impact force reduced when impact time increases |
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Term
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Definition
| Give way a little in low speed impacts so increase impact time |
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Term
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Definition
| Engine compartment dives way in front impact. Impact time increases, so force decreases |
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Term
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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 |
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Term
COLLAPSIBLE STEERING WHEEL |
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Definition
| Impact force reduced if driver hits the wheel as impact time is increased |
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Term
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Definition
Acts as cushion
increases impact time
Impact force spread over contact area with seat belt, so pressure is less on body |
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