Mechanics Flashcards
Acceleration
Rate of change of speed
Straight line —- on a distance-time graph
Stationary
Straight line —- on a speed-time graph
Constant speed
Force
A push or a pull. Measure in newtons (N)
Weight force
Due to gravity, always acts straight down
Support force
When an object pushes down a surface, the surface pushes back. Always at 90 degrees.
Thrust force
A push force. Eg from an engine
Friction force
The force that opposes motion. Always opposite direction to motion.
Buoyancy force
The upward force from a fluid (water or air)
Lift force
The upward push on a wing due to its motion through the air
Tension force
A pulling force eg from a rope or chain
Mass (m)
The amount of matter in an object, measured in kg, does not change if the object changes position
Weight (W)
Force of gravity acting upon an object. It is measured in newtons (N). It may change if the object changes position.
What does the force of gravity depend on?
The mass of the object (heavier=stronger) and the distance between the centre of the objects (closer=stronger)
What is a gravitational field?
Every object is surrounded by a force field known as a gravitational field.
What do lines on a gravitational field represent?
The direction of the gravity force that would act on a mass placed at that point, the relative strength of the gravitational field (closer=stronger)
What is a free-body diagram?
A diagram is a drawing that shows all the forces acting on an object. Arrows represent the size and direction of all forces acting.
What happens if the net forces are balanced?
Object will be stationary or constant speed
What is Newton’s first law?
An object continues in uniform motion in a straight line or at rest unless a net force acts upon in
What is Newton’s second law?
The net force on an object is proportional to the acceleration of the object. Shown by F=ma.
What is Newton’s third law?
For every action on one object, there is an equal but opposite reaction on another object.
What are the two types of friction?
Solid friction and fluid resistance
What is solid friction?
When two solid objects rub against each other, the surface aren’t completely smooth so solid friction occurs. The strength depends on the smoothness of the two surfaces.
What is fluid resistance?
When an object moves through a fluid. Also known as drag or air resistance. Depends on size /shapeof object, viscosity of liquid and speed of object.
Why is friction unwanted?
More work needs to be done to overcome forces, heats up objects, damage the surfaces due to wear
Why is friction useful?
Heats up surfaces, grips on a surface
As the speed of an object (falling) increases, what happens to the size of the air resistance?
It increases
What is terminal velocity?
When forces on a falling object are balanced and object is falling at a constant speed.
What is energy?
The capacity to do work
Conservation of energy rule
Energy cannot be created or destroyed, only converted to one form from another.
Why will a falling object never reach the calculated speed?
Some of the kinetic energy will be converted into heat energy due to friction.
What is work?
When a force moves an object for some distance, we say work is done on the object by the force
What is work equal to?
The amount of energy gained or lost
What is power?
The rate of doing work. The faster, the more powerful
