Laws of motion Flashcards
1st law
An object at rest tends to stay at rest and an object in motion tends to stay in motions at a constant speed along a straight-line path, unless an outside net force is placed upon it.
Inertia
Property of objects to resist changes in motion
Net force
When more than a single force acts on an object
Force
Push or pull
- gravitational, electrical, magnetic, muscular
- lbs and newtons
Vector quantity
A quantity such a as force that has both magnitude and direction
Mechanical equilibrium
When the net force on something is zero
- vector sum of forces equals zero
(Upward forces are + and downward forces are -)
Support force
Normal force
- upward force opposite to the force of gravity
Dynamic equilibrium
An object moving at a constant speed in a straight-line path is also in equilibrium
Equilibrium
State of no change (must be 2+ forces acting on object; cannot just be 1)
Linear motion
The simplest motion is the simplest form of motion (straight line path)
Speed =
Distance covered per unit of time
Speed = distance / time
Instantaneous speed
Speed at any instant in time
Average speed
Total distance covered / time interval
- does not indicate different speeds and variations that may take place during shorter time intervals
Velocity
Linear motion
- description of how fast and in what direction an object is moving
Vector quantity
Quantity that specifies direction as well as magnitude (such as velocity and force)
Constant velocity
Motion in a straight line at a constant speed
- must have constant speed and constant direction
Changing velocity
Either the speed or the direction (or both) change
Acceleration
How quickly velocity changes
a = change in velocity / time
- acceleration is not just the total change in velocity. It is the time rate of change, or change per second in velocity
Acceleration in a curve?
Accelerate whenever we move in a curved path (even if we are moving at a constant speed) because our direction is changing
Free fall
Lack of gravity. 10 m/s2
G on earth
9.8 m/s2
V = gt
Instantaneous velocity of an object falling from rest after a time
Distance =
1/2 a(t2)
Distance in free fall =
1/2 g(t2)
Remember
- How fast: v = gt
- How far: d = 1/2gt2
- Acceleration is not a velocity, it is the rate at which velocity itself changes
Newton’s 2nd law of motion
When a force acts on an object, the object will accelerate
F = ma
Units of F, m, and a
F = newtons (N) M = kg A = m/s2
Cause of acceleration
Is net force. An object’s acceleration is directly proportional to the force acting on it
Friction
- Forced produced when surfaces are sliding over one another
- Usually reduces the net force and the resulting acceleration
- The direction of force is always in a direction opposing motion
- Zero net force results in zero acceleration and constant velocity
- Fluid friction (air resistance)
Friction does not depend on
- Does not depend on speed. (May be more when an object is at rest and on the verge of sliding, but once sliding it remains constant)
- Area of contact
Mass
Amount of matter in an object. Measure of the inertia of a material object
Weight
Force upon an object due to gravity
Free fall
- ration of weight to mass for freely falling objects = a constant (g)
- acceleration of free fall is independent of an objects’s mass
Non free fall
Acceleration is less than g
- air drag depends on frontal area of falling object and speed of the falling object.
Terminal speed
When acceleration terminates (during non free fall)
Acceleration =
A = (mg-R)/m
3rd law of motion
When an object exerts a force on a second object, the second object exerts an equal and opposite reaction.
Action and reaction
- always occur simultaneously and act on different objects
- neither force exists without the other
Lift
The upward reaction force caused when air particles are forced down (action) and the air forces the object up (reaction)
Vector quantity
Any quantity that requires both magnitude and direction for a complete description (force, velocty, acceleration)
Scalar quantity
A quantity that can be described by magnitude only (no direction involved) (mass, volume, speed)
Vector
An arrow that represents a vector quantity - length is scaled to represent the magnitude, the direction shows the direction of the quantity
Resultant
Sum of 2+ vectors
Parallelogram rule
Construct a parallelogram whereinthe two vectors are adjacent sides, the diagonal will show the resultant
