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Various concepts related to the laws of motion, including the preparation of an astronaut docking with a satellite, the definition and classes of forces, inertial frames, and newton's first, second, and third laws. It includes examples and formulas for calculating satellite speed, time, and resultant forces.
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The astronaut orbiting the Earth in the Figure is preparing to dock with a Westar VI satellite. The satellite is in a circular orbit 700 km above the Earth's surface, where the free-fall acceleration is 8.21 m/s^2. Take the radius of the Earth as 6400 km. Determine the speed of the satellite. Determine the time interval required to complete one orbit around the Earth
answer: V =7630 m/s time= 97.4 min
l A force is that which causes an acceleration
l Also called total force, resultant force, or unbalanced force
l The acceleration is equal to zero l The velocity is constant
l The object, if at rest, will remain at rest l If the object is moving, it will continue to move at a constant velocity
l Any reference frame that moves with constant velocity relative to an inertial frame is itself an inertial frame
l A reference frame that moves with constant velocity relative to the distant stars is the best approximation of an inertial frame l We can consider the Earth to be such an inertial frame although it has a small centripetal acceleration associated with its motion
l In the absence of external forces, when viewed from an inertial reference frame, an object at rest remains at rest and an object in motion continues in motion with a constant velocity l Newton’s First Law describes what happens in the absence of a force l Also tells us that when no force acts on an object, the acceleration of the object is zero
l Force is the cause of change in motion, as measured by the acceleration
answer: 2.28x10-18^ N in the direction of motion.
l This is the vector sum of all the forces acting on the object
l Σ Fx = m ax l Σ Fy = m ay l Σ Fz = m az
l Note on notation: F AB is the force exerted by A on B
l Forces always occur in pairs
l A single isolated force cannot exist
l The action force is equal in magnitude to the reaction force and opposite in direction l One of the forces is the action force, the other is the reaction force l It doesn’t matter which is considered the action and which the reaction l The action and reaction forces must act on different objects and be of the same type
l The force F 12 exerted by object 1 on object 2 is equal in magnitude and opposite in direction to F 21 exerted by object 2 on object 1
l F 12 = - F 21
l In a free body diagram, you want the forces acting on a particular object
l The normal force and the force of gravity are the forces that act on the monitor
l A lamp is suspended from a chain of negligible mass l The forces acting on the lamp are l the force of gravity ( F g ) l the tension in the chain ( T ) l Equilibrium gives
∑ Fy^ =^0 →^ T^ −^ Fg =^0^ T^ = Fg
l The forces acting on the chain are T ’ and T ” l T ” is the force exerted by the ceiling l T ’ is the force exerted by the lamp l T ’ is the reaction force to T l Only T is in the free body diagram of the lamp, since T ’ and T ” do not act on the lamp
l Example 5.
l Conceptualize the traffic light
l Categorize as an equilibrium problem l No movement, so acceleration is zero
l Analyze l Need two free-body diagrams l Apply equilibrium equation to the light and find T 3 l Apply equilibrium equations to the knot and find T 1 and T 2
