Forces - Pressure and speed Flashcards
how to calculate pressure
pressure (Pa) = force / area of the surface
what factors affect the pressure in a liquid
- gravitational field strength
- weight of the water above the object
- molecules surrounding the object colliding
- density of liquid
how does the weight of water above an object affect the pressure in a liquid
- if the object moves deeper, the pressure due to weight will increase, as there would be more water above the object
how does density affect the pressure in a liquid
the denser the liquid, the larger the mass per unit volume, so the larger it’s weight would be
how does the gravitational field strength affect pressure
it is what determines the weight of a given mass, so a bigger gfs would mean a larger weight
what is the equation for pressure in a liquid
pressure = height of the column if liquid x density of liquid x gravitational field strength
what is upthrust
when an object has a larger upwards force from the bottom than it has a downward force from the top
what is atmosphere
a thin layer of gases that surround the Earth, made up of mostly nitrogen, oxygen, greenhouse gases
when is the atmosphere most dense
at the surface of the Earth
(at the earths surface there are the greatest number of air molecules in a given volume)
what is the relationship between pressure and atmosphere
the further away from the Earth you get, the lower the pressure, as density decreases
Why does pressure decrease as we go higher above earth
- at ground/sea level, there are a lot more particles around the object,so there will be more frequent collisions with the surface of the object, and if there are more collisions, there’ll be a greater force overall
- an object at sea/ ground level is at the very bottom of the atmosphere, so it’ll have a huge weight pressing down on it, and since weight is just a different force, it will contribute to its pressure
- the object in the air will have fewer particles above it so the force of weight will be smaller
why do mountain climbers need to carry oxygen w them
because the air is so thin, air pressure is too low
what factors affect whether or not an object will float or sink
- whether or not the force of upthrust is greater than the force of weight, if upthrust is greater, object will float, if weight is greater, object will sink
- the density of an object - a denser object will sink whilst a less dense object will float
what is the difference between speed and velocity
speed is a scalar quantity, meaning it only has magnitude
eg - 4m/s
however velocity is a vector quantity with both magnitude and direction
eg- 55m/s BACKWARDS
what is speed
- the distance the object travels in a given time
how to calculate velocity using displacement
displacement/time taken
what is the typical walking speed
1.5m/s
what is the typical running speed
3 m/s
what is the typical cycling speed
6 m/s
typical speed for a moving car
25 m/s on a motorway
13 m/s on a main road
typical speed for a moving train
55 m/s
typical speed of plane
250 m/s
speed of sound waves
330 m/s (in air)
what is acceleration
the rate of change in velocity
what is the equation for acceleration
acceleration = change in velocity / time
why can we only ever find the average acceleration, and not the exact
because over a period of time, an objects acceleration may have varied, rather than being the same
what words do we use to describe an object moving at constant acceleration
uniform
what is an objects initial velocity if it is stationary
0
How to find speed on a distance time graph
finding the gradient
what is the objects speed when there is a straight diagonal line
constant
what is the objects speed when there is a flat line
stationary
what is the speed when the line gets steeper on a distance time graph
increasing speed (acceleration)
what does a decrease in gradient in a distance time graph show
deceleration
how to find the gradient of a curved line
- draw a tangent
- pick two points and divide the rise over run
what does the gradient tell us in a velocity time graph
the acceleration
what does a constant positive gradient tell us in a velocity - time graph
that the acceleration is constant
what does a constant negative gradient tell us in a velocity time graph
that there is a constant deceleration
what does a flat line tell us on a velocity time graph
that velocity is constant
what does it mean when the line is getting steeper on a velocity time graph
rate of acceleration is increasing
how do we find the distance travelled on a velocity time graph
find the area under the curve
what can the average speed of walking etc depend on
- age
- terrain
- fitness
- distance travelled
what happens when particles collide with walls of the container
they exert a force which acts at right angles to the wall (against the normal)
what is the pressure of the atmosphere caused by
air molecules colliding with a surface
why would a crisp packet inflate when its in an aeroplane
- at ground level, the air pressure inside the bag is the same as the air pressure outside the bag
- when aeroplanes are flying, the air pressure inside the cabin is kept at a slightly lower level than the air pressure on the ground
- this means that the air pressure inside the bag is now greater than the air pressure inside the cabin, this causes the bag to inflate
when we place holes in a container, why does the bottom hole push out water the furthest
- because the water at the bottom of the container is at a higher pressure than the water at the top
why does the pressure of a liquid increase with depth
because as the depth increases, there is a greater weight of liquid acting downwards
how to explain why objects float or sink using an example
- if an object is immersed in a liquid, the bottom of the object is at a greater depth than the top of the object
- this means the bottom of the object experiences a larger pressure than the top
- because of this, there is a larger force acting on the bottom of the object than the top (there’s a resultant force acting upwards)
for an object to float, what needs to happen
the upthrust must equal the objects weight
the size of the upthrust acting on the object is the same as…
the weight of the water displaced by the object
how will an object float
if it can displace its own weight of water and the upthrust is equal to its weight
why will an object sink in water
the object cannot displace a volume of water equal to its own weight, so it sinks
- therefore the weight of the object is greater than upthrust so the object sinks
difference between distance and displacement
- distance tells us how far an object moves
- does not involve direction
DISPLACEMENT - tells us the distance that an object moves in a straight line from the start point to finish and must include direction
What affects the speed of sound?
Temperature, Sound travels faster and warmer days
what is velocity
speed in a given direction
what happens to an object moving in a circle
if its speed is constant, its velocity is constantly changing
what is acceleration
change in velocity over a given time
what is the typical acceleration from a main road to a motorway
2m/s^2
what would be the force required to move a family car from a main road to a motorway
2000N
