Transcript Slide 1
Acceleration is the rate of change of velocity. Acceleration is a vector Motion at Constant Acceleration v = v0 +at 1 2 d = v 0 t+ at 2 Falling Objects Near the surface of the Earth, due to gravity, all objects experience the same constant acceleration Falling Objects In the absence of air resistance, all objects fall with the same acceleration g = 9.80 m/s2. Newton’s First Law of Motion Newton’s first law (inertia) Every object continues in its state of rest, or of uniform velocity in a straight line, as long as no net force acts on it. Newton’s Second Law of Motion Newton’s second law • acceleration and force • acceleration is • proportional to net force • inversely proportional to mass. a Fnet / m Newton’s Third Law of Motion Newton’s third law: When one object exerts a force on a second object, the second exerts an equal force in the opposite direction on the first. Weight – the Force of Gravity Weight is not mass Weight is the force exerted on an object by gravity. Close to the surface of the Earth, where the gravitational force is nearly constant, the weight is: Normal Force An object at rest must have no net force on it. If it is sitting on a table, the force of gravity is still there; what other force is there? The force exerted perpendicular to a surface is called the normal force. It is exactly as large as needed to balance the force from the object Newtonian Gravitation gravitational force: • proportional to both masses. • decreases as the inverse of the square of the distance between the masses. Weightlessness Objects in orbit are in free fall. In free fall, you experience weightlessness: • you do have a gravitational force acting on you. • there is no normal force. This is what leads to the feeling of weightlessness. Circular Motion Instantaneous velocity is always tangent to circle. Circular Motion Centripetal acceleration, points towards the center of the circle. Circular Motion There is no centrifugal force pointing outward; what happens is that the natural tendency of the object to move in a straight line must be overcome. If the centripetal force vanishes, the object flies off tangent to the circle. tangent Kepler’s Laws Kepler’s laws describe planetary motion. 1. The orbit of each planet is an ellipse, with the Sun at one focus. Kepler’s Laws and Newton's Synthesis 2. An imaginary line drawn from each planet to the Sun sweeps out equal areas in equal times. Four Fundamental Forces 1. Gravity 2. Electromagnetism 3. Weak nuclear force 4. Strong nuclear force Problem Solving – A General Approach 1. Read the problem carefully; then read it again. 2. Draw a sketch 3. List the known and unknown quantities 4. If the problem requires algebra, do the algebra first. Once you are satisfied, put the numbers in. 5. Keep track of dimensions. 6. Make sure your answer is reasonable.