Topic 2 - Motion and Forces Flashcards
Scalar quantity
Physical quantities with magnitude only
Vector quantity
Physical quantities with magnitude and direction
Scalar examples
Speed, distance, mass, energy, temperature, time
Vector examples
Force, velocity, displacement, weight, acceleration, momentum
Velocity
Speed in a given direction
Speed(m/s)=
Distance(m)/time(s)
Distance(m)=
Average speed(m/s) x time(s)
How to interpret distance/time graphs
Gradient at a given point gives speed at that point. Use speed equation to calculate average speed by using total distance and total time on the graph.
Acceleration(m/s2)=
Change in velocity(m/s) / time(s)
Uniform acceleration is
A constant acceleration. Acceleration due to gravity is uniform for objects in free fall and its roughly 10 m/s2.U
Uniform acceleration equation
v(final velocity)2 - u(initial velocity)2 = 2 x a(acceleration) x X(Distance)
How to interpret velocity/time graphs
Gradient at a point is the acceleration. Steeper the graph, higher the acceleration. The distance under the graph shows distance travelled in that time period.
Trolley motion practical
Connect light gates along a ramp , with a trolley connected to a string at the top. At the end of the string hang a mass on a hook. Let the trolley go and use the light gates speed and time measurements to calculate acceleration
Other methods of determining the speed of objects
Rolling tape measure or stopwatch for walking speed. Video and frames per second method
Typical Walking speed
1.4 m/s
Typical running speed
3 m/s
Typical cycling speed
5.5 m/s
Typical car in city speed
13 m/s
Typical aeroplane speed
250 m/s
Typical car on motorway speed
31 m/s
Typical train speed
55 m/s
Typical wind speed
5-20 m/s
Typical speed of sound in air
340m/s
Typical ferry speed
15 m/s
Newtons first law
If the resultant force on a stationary object is 0, the onject will remain stationary. If the resultant force on a moving object is 0, it will carry on at the same velocity.
Newtons second law
Force and acceleration are directly proportional. Acceleration is inversely proportional to the object mass.
F=
m x a
Weight(N) =
mass(kg) x gravitational field strength(N/kg)
Higher gravitational field strength leads to
Higher weight. Meaning weight changes in different locations
How does speed and velocity change in an object moving in a circular motion
Speed stays constant, whilst velocity is always changing due to constant changes in direction.
What is the force that keeps an object moving in a circular motion
The centripetal force, which causes a resultant force on the object that keep it accelerating
Inertial mass
A measure of how difficult it is to change the velocity of an object. m = F/a
Newtons third law
When two objects interact, the forces they exert on each other are equal and opposite.
Newtons third law in collisions means that
If two things collide, they will accelerate depending on their mass. The higher the mass the less the forces will make it accelerate. This also explains conservation of momentum.
Newtons third law in equilibrium reactions
Gravity leads to weight pulling an object down, and the object pulls back up on the earth.
Momentum is
A property that all moving objects have that shows how hard it is to stop the object.
Momentum kg m/s (P) =
Mass(kg) x Velocity(m/s)
Conservation of momentum
The total momentum before is equal to the total momentum after in a closed system
Changes in momentum occur from?
A force acting on an object over a period of time. Newtons second law explains this.
Force(N) =
Change in momentum(kg m/s) / Time(s)
Ruler drop experiment
Tests reaction time. Hold the bottom of the ruler in line with a persons hand. Without warning drop the ruler and the other has to catch it as fast as possible. Calculate reaction time from the distance and acceleration. Typical time between 0.2-0.6s.
Stopping distance =
Thinking distance+Braking distance
Thinking distance
Distance car travels in the time between when the drivers sees the stimulus and applies the brakes.
Braking distance
Distance taken to stop once the brakes have been applied
Driver reaction time affects
Thinking distance. Inccreased by tiredness, alcohol, drugs and distractions
Speed of vehicle affects
Thinking distance because it increases distance travlled during reaction time and braking distance because it takes longer to stop
Mass of car affects
Braking distance because it increases the force needed to stop the car
State of vehicle brakes affect
Braking distance because if they are worn they wont be able to brake with as much force.
State of road affect
Braking distance becuase there may be decreased friction leading to longer for it to stop
Large decellerations are dangerous because
The less time the change in momentum occurs over, the higher the force. This means that there is more chance of injury from more forceful collisions.
As speed increases, thinking distance… and braking distance…
Thinking distance increases at the same rate, and braking distance increases by the scale factor power 2.
Energy in the cars kinetic store=
Work done by the brakes
(1/2) x (m) x (v power 2) =
F x d
