Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
PHS 112 Test 1 Review Chapters 1-4 If velocity and speed are both measures of how fast something moves, then how are they different? Velocity includes a direction vector that speed does not have. Can an object be moving and at equilibrium? What does “net force” mean? Moving or stationary the net force is zero at equilibrium. Net force refers to the sum of all the forces. Force is a vector quantity so forces often cancel each other. The amount of air resistance depends on an object’s size and an object’s speed. Air resistance is a type of friction. This force is more commonly associated with one solid object sliding across another. Do our bodies attract the earth toward us? If so, how does the force of our bodies pulling on the earth compare with the force of the earth pulling on us? We attract the earth to us with a force equal to the force of the earth attracting us. Define inertia. Resistance to change in motion/velocity. Speeding up; slowing down; turning. In the absence of air resistance, will two objects with very different masses fall at the same speed? Are they being accelerated by the same amount of force? They fall at the same speed. The more massive object requires more force to accelerate as fast as the less massive object (Law of Acceleration), and is pulled by more force, because the force of gravity is proportional to the mass. Object A falls on a table and doesn’t bounce. Object B has the same mass and falls the same distance to the table but bounces. Do they hit the table with the same amount of force? Do they hit the table with the same amount of impulse? Impulse = Ft = Δmv Without knowing the time (t) they take to stop or bounce, we cannot know the force. The object that bounces has a greater impulse because the change in velocity (v) is greater. If the acceleration of gravity on the moon is 1.6m/s2, how fast is an object falling after one second? Two seconds? How far will an object fall in one second? Two seconds? 1.6m/s; 3.2m/s; 0.8m (average speed in 1st second = 0.8m/s); 3.2m (average speed in 2nd second = 2.4m/s; 0.8m + 2.4m = 3.2m) The moon’s radius is a little more than ¼ that of earth. The moon’s mass is about 1/80th that of earth. Approximately how do each of these two differences between the earth and moon increase or decrease the gravitation on the surface of the moon compared to earth? mass1 × mass2 Decreasing the mass decreases the value of the numerator in this distance 2 proportion, which decreases the force of gravity. Decreasing the radius decreases the distance between the objects. Squaring the decrease in distance makes the denominator F∼ even smaller, which increases force. The decrease in gravity caused by the much smaller mass has a greater effect than the increase in gravity caused by the decrease in distance squared. The force of gravity on the moon is 1/6th that on earth. Two men are working on a scaffold at right. The scaffold weighs 400N, the left man weighs 300N, and the right man weighs 400N. The cable on the left end of the scaffold supports 700N. How much weight does the right end cable support? 700N Total force equals zero. 300N 300N + 400N + 400N – 700N - ? = 0 400N 400N 400N - ? = 0 , so the right cable must support 400N. The object in each drawing weighs 400N. How much force supports the weight on each rope or lever? (The lever moves 4 times farther than the object.) A 400, B 400, C 200 (ignoring weight of pulley), D 200, E 100 E A B 400 C 400 D