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Mechanical Comprehension on SIFT
Exam-Graded A
Inertia - ANSWER-An object's tendency to resist a change in motion Force - ANSWER-A push or a pull What is the unit of force? - ANSWER-Newton Mass - ANSWER-A measure of how much matter is in an object A measure of inertia of an object... An object with a larger mass will resist a change more. System - ANSWER-A collection of particles or objects that is isolated from its surroundings. All forces within a system are called internal forces, and forces outside the system are called external forces. Newton's first law - ANSWER-Law of Inertia An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force. Newton's second law - ANSWER-F=ma Force equals mass times acceleration An object in equilibrium - ANSWER-It is either at rest or moving at a constant speed. No acceleration... a= Equilibrium condition - ANSWER-When a=0; therefore, F= Newton's third law - ANSWER-For every action there is an equal and opposite reaction What are the four fundamental forces that form the basis for all other forces? - ANSWER-1. Gravitational
- Weak
- Electromagnetic
- Nuclear
Gravitational force - ANSWER-The force that pulls mass together Electromagnetic force - ANSWER-The force between electric charges. Repulsive when the charges are the same sign and attractive when the charges are opposite. Holds the positive nuclei and negative electrons of atoms together. Nuclear (or strong) force - ANSWER-Holds together the nucleus in an atom. The nuclear force has a larger magnitude than the electromagnetic force that pushes protons (positive charges) away from each other in the nucleus. Non-fundamental forces - ANSWER-Forces that can be derived from the four fundamental forces. Include weight, tension, friction, the normal force, and the buoyant force. Weight - ANSWER-The gravitational force exerted on an object (Fw) W=mg Tension - ANSWER-Pressure; stress that occurs when forces act to stretch an object (Ft or T) Friction - ANSWER-The resistance that one surface or object encounters when moving over another (Ff) Normal force - ANSWER-Occurs when an object is resting on another object (Fn or N) Always equal and opposite to the force pushing onto the surface Applied force - ANSWER-A force which is applied to an object by a person or another object (Fa) Free-body diagram - ANSWER-A diagram showing all the forces acting on an object Because all forces are vectors, it is important to consider the direction of the force when drawing a diagram What is the acceleration due to gravity? - ANSWER-g = 9.8 m/s^ Always points to the center of the earth What are the types of friction? - ANSWER-1. Static
- Kinetic
When shooting a basketball, at what point(s) will the basketball move the fastest? - ANSWER-Release point and entrance into hoop An object traveling in an arc has a velocity of zero at the top of its path and is moving slower the closer it is to that point. The object will also have the same speed at both points on the path that have the same height. So, the ball will be moving the fastest at points A and E, since both have the same height and are farthest from the top of the arc. How does the directional movement of gears look like? - ANSWER-Adjacent gear move in opposite directions Because a crowbar has a fulcrum in the middle of the effort and the resistance, it is an example of a A. first-class lever. B. second-class lever. C. third-class lever. D. first- and second-class lever. E. second- and third-class lever. - ANSWER-A A ramp is an example of: A. a lever. B. a pulley. C. a wheel and axle. D. a screw. E. an inclined plane. - ANSWER-E The amount of force that needs to be overcome for an object to move. Kinetic friction - ANSWER-Friction between moving surfaces increases with weight Buoyant force - ANSWER-The upward (vertical) force exerted by a fluid on a submerged object Magnitude of force is calculated by considering the volume of the object that is submerged in fluid Mechanical advantage - ANSWER-Ratio of the output force exerted by a machine to the input force applied to the machine. MA= (F output) / (F input) Lever - ANSWER-A simple machine that consists of a bar that pivots at a fixed point called a fulcrum; based on the concept of torque
MA = (r input) / (r output).... load/effort... effort arm/load arm What are the types of lever? - ANSWER-1. First-class... MA is dependent on EFFORT and LOAD
- Second-class... MA > 1 (E moves farther than L; multiplies force)
- Third-class... MA < 1 (multiplies distance and speed of effort) Inclined plane - ANSWER-A flat surface set at an angle or an incline with no moving parts that is able to lift objects by pushing or pulling the load. Reduces the amount of force needed to raise a mass to a certain height MA = length/height Pulley - ANSWER-A simple machine that consists of a rope that fits into a groove in a wheel MA of one pulley is 1.... MA = number of pulleys Wedge - ANSWER-Often used to separate material (e.g., knife) MA = L/W L is the length of the inclined plane on wedge W is the width (length of the back edge) Wheel and axle - ANSWER-A simple machine consisting of two circular objects of different sizes; the wheel is the larger of the two circular objects MA = (r input) / (r output) r is the radius Gears - ANSWER-Wheelwork consisting of a connected set of rotating gears by which force is transmitted or motion or torque is changed MA = [T output / T input] = [N output / N input] T is the torque from each gear N is the number of teeth on each gear Gear ratio - ANSWER-Speed ratio; the ratio of angular velocity of the input gear to the angular velocity of the output gear
A. The acceleration of A is greater than B, which is greater than C. B. The acceleration of B is greater than A but less than C. C. The acceleration of B is the same as C and less than A. D. The acceleration of A is the same as B, which is greater than C. E. All the blocks will experience the same acceleration. - ANSWER-D Blocks A and B will experience the same acceleration while they are on the incline. Both blocks will have a greater acceleration than C because gravity is increasing the net force moving the blocks down the incline. A rubber ball, a metal ball, and a wooden ball are placed in the same pot of boiling water. Which ball will have the highest temperature? A. The wooden ball will have the highest temperature. B. The rubber ball will have the highest temperature. C. The metal ball will have the highest temperature. D. The wooden and rubber balls will have the highest temperature. E. All three balls will have the same temperature. - ANSWER-C The material that transfers heat the best will have the highest temperature. Wood and rubber are insulators, and metal is a conductor; therefore, the metal will have the highest temperature. Water flows out of a water tower at a rate of 3 gallons per minute and flows in at a rate of 140 gallons per hour. After one hour, the volume of water in the tank will be A. the same. B. 20 gallons more. C. 20 gallons less. D. 40 gallons less. E. 40 gallons more. - ANSWER-D Water flows into the tower at a rate of 140 gallons per hour and out at a rate of 3 gallons per minute, or 180 gallons per hour. The tower is losing 180 - 140 = 40 gallons of water per hour. A steel ball with a temperature of 150°C is dropped into a liquid with a temperature of 120°C. Which of the following statements about the equilibrium temperature has to be true? A. The equilibrium temperature is less than 120°C. B. The equilibrium temperature is exactly 135°C. C. The equilibrium temperature is between 120°C and 150°C. D. The equilibrium temperature is greater than 150°C. E. The equilibrium temperature is exactly 270°C. - ANSWER-C Heat will transfer from the steel ball to the liquid. The equilibrium temperature depends on the masses of the objects and the specific heat of each object. Without knowing
these values, the only guarantee is that the temperatures of the objects will be somewhere between 120°C and 150°C. A 140-pound woman jumps off a 700-pound stationary raft that is in a river and travels a distance of 10 feet to right. If the water in the river is at rest, the raft will move A. 2 feet to the right. B. 2 feet to the left. C. 4 feet to the left. D. 4 feet to the right. E. 8 feet to the left. - ANSWER-B The overall momentum of the system must be conserved. The product of force and distance for the woman will be equal to the raft but in the opposite direction (left). 140(10) = 700(d) d= 1400/700 = .2 ft to the left A brake pedal with the load between the fulcrum and the effort is an example of a A. first-class lever. B. second-class lever. C. third-class lever. D. first- and second-class lever. E. first- and third-class lever. - ANSWER-B Scalars have... A. Only magnitude B. Only direction C. Both magnitude and direction D. Either magnitude or direction - ANSWER-A A scalar or scalar quantity in physics is a physical quantity that only has magnitude. Convert 1 kg to N - ANSWER-9. A simple machine has a mechanical advantage of 6. This means that A. Output force is 600% of input B. Output is unknown C. Effort is quadruple input D. Effort is six times greater than output - ANSWER-A A simple machine always has A. <100% efficiency B. 100% efficiency C. 200% efficiency D. 50% efficiency - ANSWER-A
