Download Motion, Newtons` laws, Impulse Mechanics Kinetics, kinematics

Mechanics
Motion, Newtons’ laws,
Impulse
Studies the laws of material bodies
motion.
Physical basics of Biophysics
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Dept. of Biophysics
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David Szatmári
2012. Feb.
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Kinetics, kinematics, statics
Kinematics: studies the motions itself, without of
derivation.
Kinetics: (dinamics) studies forces, regards the
interactions of affecting thinks of motion.
Statics: studies the permissions of equilibrum and
resting state of bodies.
Reference systems
Material point, masspoint
System of points
Rigid body
Kinematics of material points
Consistent linear motions
Localization: the location of material point is
identified by its coordinates.
Determine the nature and path of motion.
Velocity: derived quantity. Vector.
V = (s2 – s1)/(t2 – t1) = ∆s / ∆t
Kinetics of material point,
dinamics
Accelerating motion
Acceleration: when the velocity is changed in time.
a = ∆v / ∆t
Actual velocity: v = at
Average velocity: vs = ∆s / ∆t
The acceleration could change in time:
s = s0 + a t2 and v = v0+ a t
if not, it means consistently accelerating linear motion.
Force and mass, Newton’s II.
The acceleration of masspoint proportionally
with the affecting force and inversely
proportional with the mass of point.
F = ma basic equation of dinamics
Dinamical balance: m2/ m1 = a1/ a2
Statical balance: a = 0
Force effect, driving force, point of effect, line
of effect
Free fall, weight
Law of disability, Newton’s I.
All of the bodies are in resting state or
consistently move on linear way, until
an other body change it.
F=0
Mass: is the quantity of disability.
Kinetics studies the interaction of bodies. The
reference is the inertionsystem.
Law of interaction, Newton’s III.
If body A affects body B, B also affects A with
same amount but opposite directed force.
FA = - FB
Effect-reaction theory.
Mechanics of point system
Law of independent forces, Newton’s
IV.
If forces affect to a masspoint simultaneously,
the effect equal with the sum of vectors.
ΣF = ma
Equilibration: ΣF = 0
Impulse and force
Impulse: state of motion.
I = mv
F = ∆I / ∆t
ΣFi = ∆I / ∆t the vectorial sum of affective forces in a
closed point system, determines magnitude of
change of impulse.
Problems
Law of impulse continuity or
weightpoint.
1. A coin falls from 3 m height onto the desk.
The friction is 0.3 N force. What is the
arrival velocity of the coin? (m = 20 dkg)
If the system is not affected by outer forces, or
the sum of these is zero, the impulse of the
system is constant. It means the weightpoint
of the system consistently move on linear way
or it is in resting state.
2. A normal pilot (70 kg) has resistance for 4 g
during take off the plane. Which velocity
produce it if the take off time is 12 s?
If ΣF = 0, then I = Σmv = const., and v = const.
3. A given car (600 kg) slow down from 120
km/h to 30 km/h. What is the force which in
this time push on a normal driver (70 kg)
during 3s?