P8,P9 Flashcards
What is a scalar quantity?
- A quantity that only has a magnitude
- A quantity that isn’t direction dependent
What is a vector quantity?
A quantity that has both a magnitude and an associated direction
Examples of vector quantities
Force
Velocity
Acceleration
Displacement
Momentum
Examples of scalar quantity
Speed
Distance
Mass
Temperature
Time
How can a vector quantity be drawn and what does it show?
As an arrow
- The length of the arrow represents the magnitude
- The arrow points in the direction of the quantity
What is a force?
A push or pull on an object due to an interaction with another object
What are 2 categories that all forces can be split into?
- Contact forces
- Non contact forces
Examples of contact forces
- Air resistance
- Friction
- Tension
Examples of non-contact forces
- Gravitational forces
- Magnetic forces
- Electrostatic forces
What is weight?
The force that acts on an object due to gravity and the object’s mass
What is an interaction pair?
A pair of forces that are equal and opposite and act on two interacting objects
- Sun and Earth
What is magnitude?
Magnitude refers to the size of a numerical value
What is a physical quantity?
Something that can be measured
What is the unit used for weight?
Newton (N)
What quantities does weight depend on?
- The object’s mass
- Strength of the gravitational field at the location of the object
What is mass?
A measure of how much matter there is in an object
What quantity of an object changes depending on its location?
Weight, a 1kg mass will weigh 1.6N on the Moon but on Earth the same 1kg mass will weigh 9.8N.
What is meant by an object’s centre of mass?
The point representing the mean position of the matter in a body
What piece of equipment can be used to measure an object’s weight?
A calibrated spring-balance or newton-meter
The weight of an object and the mass of an object are said to be ____
Directly proportional
This means that if you double the mass of an object, the weight doubles too
What is the resultant force?
The overall force on an object
What is the name given to the single force that is equivalent to all the other forces acting on a given object?
The resultant force
What happens when a force moves an object through a distance?
Energy is transferred and work is done on the object
What happens when work is done against frictional forces?
- A rise in temperature of the object occurs
- Kinetic energy is converted to heat
Why does air resistance slow down a projectile?
It acts just like friction does working against the object. Kinetic energy is converted into heat, slowing down the object
What is it called when the forces acting on an object combine to give a resultant force of zero?
Equilibrium
What are the 3 things that can happen when a force is applied to a object?
- Stretch
- Bend
- Compress
Explain the relationship between the force applied and the extension of an elastic object
The extension is directly proportional to the force applied, provided that the limit of proportionality is not exceeded
What are the 2 types of change in shape or deformation?
- Elastic
- Plastic
What is elastic deformation?
When an object returns to the original shape and length after the force has been removed
What is plastic or inelastic deformation?
When an object doesn’t return to its original shape and length after the force has been removed
Examples of objects that undergo elastic deformation
- Rubber bands
- Spring
What type of energy is stored in a spring when it is stretched/compressed?
Elastic potential energy
What is the limit of proportionality?
- The limit of proportionality refers to the point beyond which Hooke’s law is no longer true when stretching a material.
- It is the furthest point an elastic material can be stretched or deformed while being able to return to its original shape.
To investigate the relationship between force and extension for a spring (6 mark)
- Secure a clamp to the stand
- use bosses to attach two clamps to the stand
- attach the spring to the top clamp and ruler to the bottom
- adjust ruler so it is vertical and with 0 at top of spring
- measure and record unloaded length of spring
- hang 100g
- repeat 7 till you have 1000g
What is moment?
The turning effect of a force
What do you have to do to an object to get the maximum moment?
You need to push at right angles (perpendicular)
What is pressure?
Force per unit area
What are gears and what do they do?
Gears are circular discs with “teeth” around their edges that interlock, so that turning one causes another to turn in the opposite direction
If an object is in equillibrium, what can be said about the moments acting on the object?
The clockwise moments are equal to the anticlockwise moments.
What is the unit for pressure?
Pa
What determines the moment of a gear wheel?
The size of the wheel
What is meant by the term “fluid”?
A liquid or a gas
How does pressure in fluids increase with depth?
As the depth of the liquid increases, the number of particles above that point increases. The weight of these particles adds to the pressure felt at that point, so liquid pressure increases with depth.
Explain why atmospheric pressure decreases with an increase in height
- Pressure is created by collisions of air molecules
- The quantity of molecules decreases as the height increases
- This results in atmospheric pressure decreasing as their are less collisions
How can the density of a liquid be described?
It is uniform (the same everywhere) and it doesnt vary with shape or size
What is upthrust caused by in a liquid?
Upthrust is caused by a pressure that is larger on the bottom of an object than it is on the top of an object submerged in a liquid
What is upthrust equal to?
The weight of the fluid that has been displaced by an object.
E.g the upthrust on a pineapple in water is equal to the weight of a pineapple-shaped volume of water
What happens if the upthrust is equal to the weight?
The forces balance meaning the object floats
What factors influence whether an object will sink or float?
- Weight
- Upthrust
- Density of fluid
Explain why an object with a density greater than that of water can never float
It the density of the object is high, there would not be enough volume displaced to produce an upthrust larger than the object’s weight. This means that it will sink.
How do submaries make use of upthrust?
To sink, large tanks are filled with water to increase the weight of the submarine so that its weight is more than the upthrust. To rise to the surface, the tanks are filled with compressed air to reduce the weight so that it is less than the upthrust.
What is distance?
Distance is just how far an object has moved. It doesn’t involve direction.
Distance is vector/scalar, Displacement is scalar/vector
Distance is scalar, Displacement is vector
What is the displacement if you walk 5m north then 5m south?
Displacement = 0m but distance travelled = 10m
What is displacement?
Displacement is a vector quantity. It measures the distance and direction in a straight line from an object’s starting point to its finishing point - e.g the plane flew 5m north.
What is velocity?
Speed in a given direction
e.g 30 mph north
What is speed?
Speed is just how fast an object is travelling with no regard to the direction
Speed is scalar/vector, Velocity is scalar/vector
Speed is scalar, Velocity is vector
Example of an object travelling at a constant speed and constant changing velocity
A car going around a roundabout
What is uniform acceleration?
Speeding up or slowing down at a constant rate
What is acceleration?
Acceleration is the change in velocity in a certain amount of time
What is deceleration?
The rate at which an object slows down also known as negative acceleration
How can speed be calculated from a distance-time graph?
The speed is equal to the gradient of the graph
How can the distance travelled by an object be calculated from a velocity-time graph?
It is equal to the area under the graph
Give an approximate value for the acceleration of an object in free fall under gravity near the Earth’s surface
9.8m/s^2
What do flat sections on a distance-time graph show?
The object is stationary/stopped
What do flat sections on a velocity-time graph show?
The object is travelling at a steady/constant speed.
What direction does friction always act in?
Opposite direction to movement
In terms of friction, what do you need to do to travel at a steady speed?
- The driving force needs to balance the frictional force
- Frictional forces always increase with speed
What is drag?
Drag is the resistance you get in a fluid
What is air resistance a type of?
Drag
What is the most important factor in design to reduce drag and why?
- Keeping the shape of the object streamlined
- This is where the object is designed to allow fluid to flow easily across it, reducing drag
What is terminal velocity?
When a falling object has reached its maximum speed and will then fall at a steady speed
