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Mechanics Motion, Newtons’ laws, Impulse Studies the laws of material bodies motion. Physical basics of Biophysics - Dept. of Biophysics - David Szatmári 2012. Feb. - 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?