5 - forces Flashcards
whats vector and examples
magnitude and direction
- force/velocity/displacement/accelaration/momentum etc…
whats scalar and examples
only has magnitude (no direction)
- speed/distance/mass/temp/time etc….
whats a contact force and examples
2 objects need to be touching for a force to act
- friction/air resistance/ normal contact force
whats a NON contact force and examples
objects don’t need to be touching for a force to act
- magnetic/electrostatic/gravitational
effects of gravity
- gives everything a weight
- makes everything fall to the ground on earth
whats mass
- the amount of stuff inside an object
- the same anywhere in the universe
what is weight
- the force acting on an object due to gravity
- depends on the gravitational field strength so varies in different locations
how to calculate the resultant force on a free body diagram
- horizontal and vertical
- large value - smaller value
whats work done
the amount of force needed to move an object a certain distance
when is an object in equillibrium
if all the forces acting upon it give a resultant force of 0
elastically deformed and inelastically deformed
- can return to original shape and length after the force has been removed
- cant return back to its original shape and length after the force has been removed
what is the moment and how do you get a larger one
- the rotational or turning effect of a force
- eg spanner turning around a nut (pivot)
- larger force and longer distance from pivot would mean a larger moment
whats a lever
- increases the distance from the pivot at which the force is applied - less force for the same moment
- basically they make it easier to do work eg like a load or turn a nut
what are gears
- circular discs with ‘teeth’ around the edges
- their teeth interlock so turning one turns another in the opposite direction
- large gear = bigger moment bc distance from pivot is larger
- larger gear will turn slower than smaller gear
what’s the pressure of a fluid
a force is exerted at right angles to any surface in contact with this fluid
whats the effect of depth of the pressure of a liquid
the pressure increases bc the number of particles above that point increases
whats upthrust
- a force that pushes upwards on an object submerged in a fluid
- equal to the weight of the fluid that has been displaced by the object
effect of weight of an object and upthrust
if weight is more than the upthrust the object skins
if the weight is less than the upthrust the object floats
how do submarines sink and float
- SINK - large tanks are filled w water to increase weight so sub is more than upthrust
- FLOAT - tanks filled w compressed air to reduce weight so sub is less than upthrust
whats the relationship between atmospheric pressure and height
the altitude (height above earth) increases as the atmospheric pressure decreases
distance and displacement
- scalar - how far an objects moved
- vector - distance and direction from starting point to finishing point
speed and velocity
- scalar - how fast you are going
- vector - how fast you are going at what direction
whats happening when objects move in a circle
constant speed but changing velocity (changing direction but at the same pace)
every day speeds of walking/running/cycling/car/train/plane
walking - 1.5 m/s
running - 3 m/s
cycling - 6 m/s
car - 25 m/s
train - 55 m/s
plane - 250 m/s
whats wind speed effected by
- temp
- pressure
- obstacles - large buildings
whats human speed effected by
- old age
- fitness
- distance travelled
- terrain
whats acceleration
the change in velocity in a certain amount of time (how quickly you are speeding up)
whats deceleration
the negative of acceleration (if something slows down the change in velocity is negative)
distance time graph
- gradient = speed (steeper the faster)
- flat = stationary (its stopped)
- curves in gradient = acceleration/ deceleration
- straight line gradient = steady speed
if an object is changing speed on a DISTANCE time graph - how can you find its speed at a specific point
draw a tangent to the curve at that point
velocity time graphs
- gradient = acceleration
- flat = steady speed
- curves in gradient = changing acceleration
how do you find the distance travelled from a VELOCITY time graph
find the area under that section
whats friction
the force that acts in the opposite direction to movement
whats drag
resistance you get in a fluid - eg air resistance is a type of drag
how do you reduce drag
keep objects streamlined
how does an object reach terminal velocity
- when objects start to fall - force of gravity is more than the frictional force slowing it down - it accelerates
- as the speed increases friction builds up
- this gradually reduces acceleration until frictional force is equal to the accelerating force
what is terminal velocity
- resultant force of 0
- fall at a steady speed
- falling object —> frictional force is equal to the accelerating force
newtons first law
“if the resultant force of a stationary object is 0, the object will stay stationary. if the resultant force on a moving object is 0 it will carry on moving at the same velocity” ——> resultant force is needed to make something start moving/speed up/slow down etc
newtons second law
- force and acceleration are directly proportional
- the larger the resultant force acting on an object, the more the object accelerates
- acceleration and mass are inversely proportional
- object with a larger mass will accelerate less
- F = ma
whats inertia
when objects move at a steady speed they stay moving at a steady speed - this tendency to continue in the SAME STATE OF MOTION is called inertia
what does inertia mass tell you
how difficult it is to change the velocity of an object
newtons third law
- “when 2 objects interact, the forces the exert on each other are equal and opposite”
example of man pushing on wall - newtons third law in EQUILIBRIUM
- man pushes wall
- normal contact force acts back on him
- these forces are the same size
- as man pushes the wall the wall pushes back with an equal force
different between newtons third law and newtons third law in eq
- normal 3rd law –> exerting equal and opposite but if one has a smaller mass it will accelerate away further
- eq - northing ever moves bc forces are equal
equation for stopping distance
thinking distance + breaking distance
what is thinking distance
how far the car travels during the drivers reaction time
what is braking distance
distance taken to stop under the breaking force
factors that effect thinking distance
- speed your going at - the further u will travel during ur thinking time
- reaction time - the longer ur reaction time the longer your thinking distance
factors that effect braking distance
- speed - the faster the car moving the longer it will take to stop
- weather/road surface - wet or icy - skids
- condition of tyres - bald tired cant get rid of water in wet conditions - skidding
- condition of brakes - worn/faulty - wont be able to apply as much force
what happens when you push the brake pedal of a car
- push the brake pedal which causes the brake pads to press onto the wheels
- this contact causes friction which causes work to be done
- this work done btwn brakes and wheels transfers energy from kinetic energy stores of the wheels to the thermal energy stores of the brakes
- the brakes increase in temperature
how to measure reaction time
the ruler drop test - practical
what is momentum
- greater the mass of an object , the greater its velocity = it has more momentum
- vector
- mass x velocity
conservation of momentum
in a closed system the total momentum before an event is equal to the total momentum after the event
what safety features do cars have
- crumple zones - crumple on impact increasing time taken for car to stop
- stretchy seatbelt
- air bags
how do bike helmets protect us
- crushable layer of foam - reduces impact on brain
how do crash mats protect us
- cushioned playground flooring - soft and compressible
