Forces Flashcards
Resultant force
Two or more forces acting on an object can be replaced by a single for with the same effect
Eg) <—200N 400N—> = —>200N
Newton’s first law
If the resultant force acting on an object is 0, then its acceleration will be 0
Newton’s second law
An object will accelerate if there is a resultant force. Acceleration is directly proportional to resultant force, inversely proportional to mass
Newton’s third law
Forces on interacting objects are equal an opposite
Distance time graphs
Speed (m/s) = distance (m) / time (s)
Gradient = speed
Velocity time graphs
Gradient = acceleration
Area = distance
Acceleration
Acceleration (m/s^2) = v-u (m/s) / time (s)
Change in velocity
v-u^2 = 2 x a x d
Gravitational field strength
g (N/kg) = weight (N) / mass (kg)
Stopping distance
Stopping distance = thinking distance + breaking distance
What does breaking distance depend on?
-road material
-weather
-friction
What does thinking distance depend on?
-drugs
-alcohol
-tiredness
Average person has a reaction time of 0.7s
Change in momentum
Force (N) = m x v-u / time
Factors that decrease change in momentum
-seatbelts
-crumple zone
Momentum
Momentum (kg m/s) = mass (kg) x velocity (m/s)
Conservation of momentum
In a closed system, the total momentum before any event is equal to the total momentum after
Falling objects
Initially, there is a resultant force downwards as her weight is greater than the air resistance. She accelerates. The air resistance then increases as she accelerates so the resultant force decreases until it reaches zero and we have reached a constant velocity. This is called the terminal velocity
Core practical - how the acceleration of an object is affected by the resultant force and mass
Resultant force
-independent variable = resultant force
-dependant variable = acceleration
-control variable = mass
Mass
-independent variable = mass
-dependant variable = acceleration
-control variable = resultant force
