Mechanics Flashcards
Define Moment
It is the turning effect of a force. It can be explained by the equation: Moment = Force x perpendicular distance from the pivot.
Unit of Moment
Newton meter (Nm)
What is Couple?
A pair of equal and opposite Copland forces that has a turning point but no resultant force.
Define Center of Mass.
The point at which the weight of the object may be considered to act.
Discuss an object stability using the Center of Mass.
An object is stable when its center of mass is inside its base (it will topple if its center of mass is outside its base). The wider base an object has, the lower its center of mass, the more stable it is.
Using your knowledge of the centre of mass, explain why would a forklift truck be better carrying its load close to the ground, rather than higher up in the air.
As the mass of the load is lowered towards the ground, the centre of mass of the load and the truck moves towards the ground. This improves the stability of the load and forklift truck.
Define Displacement.
The distance moved by an object in a specific direction (Vector quantity).
Define Velocity.
The rate of change of displacement.
What is instantaneous velocity?
The specific velocity of an object at a specific point in time. It can be found from a displacement-time graph by drawing a tangent to the graph at the specific time and calculating the gradient.
What is average velocity?
The velocity of an object over a specific time. It can be found by dividing the the final displacement by the time taken.
Define acceleration.
The rate of change of velocity of an object.
Displacement-Time Graph.
Gradient: velocity
Area under graph: MEANINGLESS
Y-intercept: initial displacement
Straight line: constant velocity
Curved line: acceleration
Horizontal line: stationary
Velocity-Time Graph.
Gradient: acceleration
Area under graph: displacement
Y-intercept: initial velocity
Straight line: uniform acceleration
Curved line: non uniform acceleration
Horizontal line: constant velocity
Acceleration-Time Graph
Gradient: MEANINGLESS
Area under graph: change in velocity
Y-intercept: initial acceleration
Straight line: constant acceleration
Curved line: none
Horizontal line: stationary
What Force would act on an object in free fall?
If an object is in free fall, then the object’s weight is the only force acting on it. It will accelerate at a constant rate. This constant rate is called the acceleration due to gravity (g).
What is drag?
Drag is a frictional force experienced by objects that travel through liquid or gas. The faster an object moves through a medium, the larger the drag.
What happens to projectile motion if air resistance isn’t negligible?
The horizontal component of the velocity of a projectile decreases which means that both its range and maximum height is decreased compared to no air resistance.
State Newton’s First Law.
An object will remain at rest or continue moving with constant velocity unless acted on by a resultant force.
State Newton’s Second Law.
The resultant force on an object is equal to its rate of change in momentum
(Or)
The resultant force on an object with constant mass is directly proportional to its acceleration.
F (resultant force) = m (mass) x a (acceleration)
State Newton’s Third Law.
If body A exerts a force on body B, then body B will exert a force on body A of equal magnitude but in the opposite direction
Rules on Newton’s third law pairs:
- The two force pairs must act on two different objects.
- Must be of the same type.
- Must have the same magnitude but opposite direction.
What does it mean by closed systems?
Systems with no external forces may be described as ‘closed’ or ‘isolated’
Principle of Moments
For a system to be in equilibrium, the sum of the clockwise moment is equal to the sum of the anti-clockwise moments
Impulse
The rate of change of momentum
Work done
The amount of energy transferred when an external force causes an object to move over a certain distance.
Power
The rate of doing work
Efficiency
The ratio of useful power output from a system to its total power input
Principal of Conservation Of Energy
Energy cannot be created or destroyed, it can only be transferred from one form to another
Density
Mass per unit volume
A material obeys Hooke’s law if:
The extension of the material is directly proportional to the applied force up to a limit of proportionality
Limit of Proportionality
The point in which beyond it, Hooke’s law is no longer true
Elastic Limit
The point in which beyond it the material would be permanently deformed and cannot go back to its original shape
Tensile Stress
The force exerted per unit cross sectional area of a material
Tensile Strain
The extension per unit length. It has no unit.
Breaking Stress
A maximum stress a material can stand before it fractuares (breaks).
A material with high breaking stress is considered ductile, which means it can extend more before breaking because of plastic deformation.
Difference between brittle and ductile
Brittle materials have very little to no plastic region.
Ductile materials have a larger plastic region.
Young Modulus
The ration of tensile stress and tensile strain
