2. Mechanics Flashcards
Define displacement
The length and direction of the line segment joining the initial and final positions of an object
Define velocity
Rate of change of displacement
Define acceleration
Rate of change of velocity
What is the acceleration for an object travelling in the positive direction (speeding up/slowing down)?
Speeding up: Positive acceleration
Slowing down: Negative acceleration
What is the acceleration for an object travelling in the negative direction (speeding up/slowing down)?
Speeding up: Negative acceleration
Slowing down: Positive acceleration
Define positive acceleration
Velocity increasing/velocity decreasing in opp. direction
Define negative acceleration
Velocity decreasing/velocity increasing in opp. direction
What does the area under an acceleration-time graph show?
Change in velocity
Velocity may not start from zero
What are the 2 assumptions made in the kinematics equations?
- Acceleration is constant
2. When t=0, s=0
What 2 factors cause air resistance (AR) to increase?
- An increase in mass
2. An increase in speed
Define terminal velocity
The constant velocity reached by a falling object when the drag force equals in magnitude to the force that is accelerating the object
(fluid resistance is the horizontal version of this)
Define drag force
The retarding force due to air resistance
Directly proportional to the speed of the object
What does a ‘projectile motion’ graph look like?
A parabola
Difference between a no-AR graph and an AR-graph for projectile motion?
- Non-symmetrical
- Lower max height
- Shorter range
- Travels further horizontally on the way up than the way down
Describe the motion of a projectile, both horizontal and vertical
Horizontal: Uniform velocity
Vertical: Uniform acceleration
What are the 3 different types of fields, and what do they each act on?
- Gravitational - Acts on mass
- Electric - Acts on charges
- Magnetic - Acts on moving charges
State Newton’s first law of motion
An object at rest will remain at rest and an object in motion will continue in motion at constant speed in a straight line in the absence of a net force acting on it.
State Newton’s second law of motion
The rate of change of momentum of a body is directly proportional to the net force acting on it and takes place in the direction of the force.
What affects inertia?
Mass
What is a state of inertia
An object’s resistance to a change in the state of rest or motion of the body, when a force is applied
State Newton’s third law of motion
When two bodies A and B interact, the force that A exerts on B is equal and opposite to the force that B exerts on A.
2 rules for action-reaction pairs
- Must be the same kind of force (contact/gravitational/magnetic…)
- Must act on 2 different bodies
Define static friction
The friction that exists between a stationary object and the surface on which it is resting
Define dynamic friction
The friction between surfaces moving relative to each other
What does Fmax depend on (2 factors)
The nature of the 2 surfaces in contact
The normal reaction between the 2 surfaces
Define work
The force multiplied by displacement in the direction of the force
Define kinetic energy
The energy an object possess by virtue of being in motion
Define potential energy
The energy possessed by objects due to their position or condition
Define gravitational potential energy
The amount of work done in order to raise the body to the height h from a reference level
What is the Principle of Conservation of Energy? [3]
- Energy cannot be created or destroyed
- Can only be converted from one form to another
- Total amount of energy in a closed system remains constant
Define mechanical energy
The sum of an object’s KE + PE
The energy due to an object’s position and motion
Define efficiency
The ratio of the useful energy output to the energy input
Define power
The rate of doing work
Define linear momentum
The product of an object’s mass and velocity
Define impulse
The change in momentum caused by a force
What does the area under a force-time graph represent?
Impulse
State the law of conservation of momentum
The total momentum of a closed system is constant, provided no external resultant force acts on it
State the 3 kinds of collisions
Elastic
Perfectly inelastic
Inelastic
State the characteristics of an elastic collision
Total KE & momentum conserved
When one body ‘A’ collides into a stationary one ‘B’, ‘A’ stops moving and ‘B’ starts moving
Think: Newton’s Cradle
State the characteristics of a perfectly inelastic collition
Total momentum conserved but total KE not conserved
When the bodies collide, they become one
State the characteristics of an inelastic collision
Total momentum conserved but total KE not conserved
State the characteristics of an explosion
Total momentum remains constant after the explosion at 0
2 bodies travel in opposite directions to cancel out momentum
