Forces, Motion And Energy Flashcards
(38 cards)
Resultant force
Whenever two bodies interact, the forces they exert on each other are opposite and equal
When a ball falls through fluid
Beggining: stationary, only weight acts on the ball
Middle: increasing speed (resistive force increases as the speed increases, causing the acceleration of the ball to decrease)
End: terminal velocity (weight equals upward resistive force and acceleration is zero)
The arrows level out.
Kinetic energy
Movement
When a car breaks
The speed decreases and this reduces the kinetic energy. It is convert into other forms of energy.
If a mass is dropped
The gravitational potential energy is converted into kinetic energy
Gpe= ke
Gh = 1/2mv2
As an object falls through a fluid such as air
It collides with air molecules and pushes them out of the way.
When ke strikes the ground
It gets converted into other forms such as heat and sound
Work done is equal to
Energy transferred
To stop a veichle
Breaking force is needed.
Stopping time depends on
Reaction time and braking time
Stopping distance depends on
Thinking distance and braking distance
When a veichle travels at a steady speed
The frictional forces balance the driving force
A drivers reaction time can be affected by
Tiredness, drugs, and alcahol. These will increase the reaction time.
A veichle braking distance can be affected by
Adverse road and weather conditions (e.g ice, water or oil on the roads)
And the poor condition of the veichle (defective brakes or no tread on tyers)
The breaking distance is also affected by the
Mass and speed of the veichle
On a velocity- time graph
The flat bit is the thinking time and the slope is the braking time
When a stretching force is applied to an object
It’s shape and size can be altered and the object is said to be deformed
This deformation can be elastic or plastic
Elastic deformation
The object will return to its original shape and size, once the force is removed
Plastic deformation
The object will not return to its original state and size, once the stretching force is removed
When a spring is loaded
It initially undergoes elastic deformation but if the load is increased above its elastic limit, the spring will undergo plastic deformation
Extension
The amount by which the spring stretches
Hookes law
Provided the stretching force acting on an object does not extend the elastic limit, the extension of the object is directly proportional to the stretching force
when something falls
the weight of the object is constant and acts downwards causing the object to fall
as the object falls, it collides with the fluid particles which exert frictional forces (drag) on the object
as the speed of the object increases, it collides with the particles more frequently
frictional forces increase in this way until they balance the weight
when the weight equals the frictional forces, the forces are balanced and the resultant force is zero
no object no longer accelerates
the object continues to fall at its terminal velocity
if an object collides with the ground the kinetic energy is converted into
sound and heat energy
