section 1: Forces and motion Flashcards
important units:
-kilogram (kg)
-metre (m)
-metre/second (m/s)
-metre/second²
-newton (N)
-second (s)
-newton/kilogram (N/kg)
speed:
-> the distance travelled per unit time
-if the speed of something is changing, it is accelerating
-acceleration of free fall near to the earth is constant
distance-time graphs:
-the gradient is the velocity
-negative gradient = object is returning back to the starting point
-horizontal line = means object is stationary
-if distance is 0 = object is at the starting point
-curved line = means that the velocity is chaniging, and it is accelerating
formula linking average speed, time and distance:
average speed = distance moved/ time taken
practical: investigate the motion of everday objects such as toy cars or tennis balls
- Set up aparatus
- Mark a line on the ramp-this is going to make sure the car starts at the same point each time
- Measure the distance between each light gate-you’ll need this to find the car’s average speed
- Let go of the car just before the light gate so that it start to roll down the slope
- The light gates should be connected to a computer. When the car passes through each gate, a beam of light is broken and a time is recorded by data-logging software
- repeat this experiment several times and get an average time it takes for the car to reach each light gate
- using these times and the distances between gates you can find the average speed of the car on the ramp and the average speed of the car on the runway-just divide the distance between the light gate by the average time taken for the car to travel between gates
velocity and acceleration:
-velocity: is the speed in a given direction
-acceleration: is the change in velocity per unit time
formula linking acceleration, change in velocity and time taken
acceleration = change in velocity/time taken
a = (v-u)/t
velocity-time graphs:
-the gradient is acceleration
-negative gradient (i.e. negative acceleration) = deceleration
-if speed is zero = it is at rest
-horizontal line = means constant speed
-the area under the line = distance travelled
-curved line = means that the acceleration is changing
formula linking final speed, initial speed, acceleration and distance moved:
(final speed)² = (initial speed)² + (2 x acceleration x distance moved)
v² = u² + (2 x a x s)
effects of forces:
-forces can change the speed, shape or direction of a body and they are measure in Newtons (N)
-there are various types of forces (e.g. gravitational, electrostatic)
vectors and scalars:
-vector: have magnitude and direction
examples: displacement, velocity, acceleration & force
-scalar: has just magnitude
examples: distance, speed, time & energy
finding the resultant force:
-to find the resultant of two or more forces acting along the same line, they should be added together if in the same direction and subtracted if in the opposite direction
friction:
-> is a force between two surfaces which impedes motion and results in heating
-air resistance is a form of friction
Newton’s first law:
-Newton’s first law states that an object has a constant velocity unless acted on by a resultant force
Newton’s second law:
-states that:
force = mass x acceleration
f = ma
mass and weight:
-mass: is a measure of how much matter is in an object, measured in kilograms (kg)
-weight: is a gravitational force (the effect of a gravitational field on a mass)
weight = mass x gravitational field strength
w =mg
-the gravitational field strength on earth is 10N/kg
motion of a body falling in a uniform gravitational field: terminal velocity
-initially, there is no air resistance and the only force acting on it is weight
-as it falls, it accelerates which increases its speed and hence air resistance
-this causes the resultant force downwards to decrease
-therefore, the acceleration decreases, so it is not speeding up as quickly
-eventually they are equal and opposite and balance so there is no resultant force
-so, there is no acceleration and the terminal velocity is reached
factors affecting vehicle stopping:
-the distance travelled in the time between the driver realising he needs to brake and actually pressing the brakes is called the thinking distance
-factors which increase the thinking distance include:
-greater speed
-slower reaction time due to alcohol, tiredness or distractions. Reaction time can also be increased by caffeine, which reduced the thinking distance
-the distance travelled in the time between pressing the brakes and the vehicle coming to a stop is called the braking distance
-factors which increase the the braking distance include:
-greater speed or mass
-poor road conditions (icy, wet) or car conditions (worn tires, worn brake pads)
-the stopping distance is the sum of the thinking distance and braking distance
practical: investigate how extension varies with applied force for helical springs, metal wires and rubber bands
- using the ruler, measure the initial length of the first spring when no force is applied
- set up the spring so it is hanging securely from the clamp stand
-you can also secure the ruler to the clamp to ensure it does not move at all during the experiment - add one of the masses and record the extension of the spring
-the extension is the difference between the new length and the initial length - continue adding masses and recording the extension each time
- plot a graph of force applied against the extension of the spring
-force can be calculated from mass x gfs (i.e. 10 x the mass hanging on the spring)
-the gradient of the line of best fit will be the spring constant as k = F/x - using this value, you can calculate the work done each time the spring extends
-use the formula: W = 1/kx²
Hooke’s Law:
-states that for a spring, F = kx where F is the force applied to the spring, k is the spring constant, and x is the extension
Hooke’s Law: graphs
Linear (straight line) force (y-axis) -extension (x-axis) graph:
-elastic deformation following Hooke’s law
-the point it stops being linear is called the limit of proportionality, from the on, it does not obey Hooke’s law
-gradient is the spring constant, k
Non-linear (curved line) force-extension graph:
-deformation not following Hooke’s Law
-after this region, it will fracture
