Physics - Motion & Pressure Flashcards
What is speed?
The measure of how far something travels in a particular time
How do you calculate speed?
distance travelled (m) ------------------------------ time taken (s)
What is instantaneous speed?
The speed of an object at a particular moment in time
How do you work out average speed?
total time
What is relative motion?
How fast one object is travelling compared to another
What is the relative speed of two objects moving at the same speed in the same direction?
zero
What is the relative speed of two cars moving at 30mph towards each other?
60mph
What does a distance-time graph show?
The distance that an object travels over a certain time
What does a steep line show you?
The object is moving fast
What produces gas pressure?
The amount of collisions between the air molecules and their container
How can you increase pressure?
By squashing a gas into a smaller volume, which causes more collisions
What makes the size of a balloon increase?
When there are more collisions in the inside than the outside
What happens when the temperature of a gas decreases?
Its molecules move slower and fewer collisions occur with the sides of the container
What happens to the pressure of a solid container when the gas pressure decreases?
It decreases
What do the molecules do when the temperature of a gas increases?
They collide more and are much faster
What happens when more gas is added to a container?
The gas inside becomes compressed
What happens when a gas is compressed?
As more molecules are added in the same space, more collisions occur
Why is a stronger container needed to hold a compressed gas?
The pressure is bigger, so the force exerted by the gas over the area of the container is bigger
What is atmospheric pressure?
The pressure that the air around you exerts
Why is the atmospheric pressure at sea level higher than at a mountain?
Gravity pulls the air particles towards the Earth, and because they are closer more collisions occur, increasing the pressure
Why does gas have a higher density at sea level?
There is more mass of gas in a certain volume
What are oxygen tanks?
Tanks that contain oxygen gas compressed into a small volume
What happens when liquid pressure occurs?
Water molecules push on each other and on surfaces in all directions
Why are liquids incompressible?
Because the liquid particles are touching each other with very little space between them and pass on any pressure
Why are gases compressible?
There is lots of space between the gas particles
What does pressure at a certain depth depend on?
The weight of the water above it
What causes upthrust and what does it do?
Upthrust is caused by liquid pressure and acts on any object that is floating, or is submerged in a liquid
Why does a rubber duck float and what is produced?
More water molecules hit the bottom of the rubber duck than there are air molecules hitting the top, which produces upthrust
When would an object not be able to float?
If the area in contact with the water is too small, there is not enough upthrust to balance its weight so it sinks
What force is required to push a submarine up and how is it produced?
Upthrust is produced as underwater there is a difference in pressure between the top and bottom of the submarine
What is pressure?
A measure of how much force is applied over a certain area
What direction does pressure act in?
90°, or normal, to the surface
How do you calculate pressure?
area (m^2)
Why do the studs on the bottom of a football boot have a smaller area compared with the area of the foot?
In order to produce a bigger pressure, which makes the studs sink into the ground and move quicker as well as stronger grip
Why do snowshoes require a big area?
It lessens the pressure on snow so that you do not sink
What does a turning force’s distance depend on?
A pivot
What is the turning effect of a force and what does it depend on?
A moment, which depends on the force being applied and how far away it is from the pivot
How do you calculate a moment?
moment (Nm) = force (N) x perpendicular distance from the pivot (m)
How does the moment of your weight act?
Anticlockwise
What is the law of moments?
When an object is in equalibrium the sum of the clockwise moments is equal to the sum of the anticlockwise moments
What is the centre of gravity (mass)?
The point where all the weight of an object acts through
What will happen if the centre of gravity is above the pivot?
There will be no turning force
What will happen if the centre of gravity is to the left or right of the pivot?
There will be a turning force
