chapter 4 - dynamics II

Question 1

newton’s 1st law

Answer 1

every object will continue in its state of rest or uniform motion in a straight line unless a resultant force acts on it

Question 2

inertia

Answer 2

reluctance of the object to change its state of rest or motion, due to its mass

Question 3

newton’s 2nd law

Answer 3

when a resultant force acts on an object of a constant mass, the object will accelerate in the direction of the resultant force

Question 4

newton’s 3rd law

Answer 4

if body A exerts a force on body B, body B will exert an equal and opposite force on body A

Question 5

friction

Answer 5

contact force that opposes motion

Question 6

terminal velocity

Answer 6

when the air resistance acting on object equals its weight, it will start travel at a constant speed (zero acceleration)

Question 7

effects of a force applied on an object

Answer 7

• change of direction/speed of an object
• make a stationary object move
• stop a moving object

Question 8

common action reaction pair?

Answer 8

weight of object due earth + gravitational force on earth by object which is equal in magnitude but in opposite directions and acts on different bodies

Question 9

factors affecting friction

Answer 9

type of surface area and weight pressing down, but not area of contact

Question 10

advantages and disadvantages of friction

Answer 10

advantages : magnetic levitation, disadvantages : wear and tear

Question 11

how to reduce friction?

Answer 11

ball bearings, lubrication, air cushion

Question 12

explain the process of terminal velocity

Answer 12

1. falling object will accelerate initially due to their weight and will have very little air resistance
2. as the velocity of the object increases, air resistance also increases. This causes the resultant force acting on the object to decrease. when resultant force decreases, acceleration also decreases. therefore, velocity increases at a decreasing rate, and acceleration is non-uniform and decreasing.
3. when the air resistance increases to the same magnitude as the weight, the forces are balanced and the resultant force is zero, resulting in zero acceleration. the object falls with constant velocity, aka terminal velocity.
4. when the parachute is open, it drastically increases the surface area of the falling object, causing the air resistance to increase. the air resistance increases beyond the weight, and the resultant force will act upwards (upwards force is greater). the object will then decelerate uniformly and the velocity decreases at a constant rate.
5. as the velocity decreases, air resistance will also decrease. when it reaches the same magnitude as the weight, terminal velocity occurs again as resultant force is now zero.
6. the object lands and velocity reaches zero.

Question 13

why is acceleration not constant?

Answer 13

when initial force was exerted, it was greater than the water resistance, therefore causing the object to accelerate. as the speed of the object increases, the water resistance also increases to eventually reach the same magnitude as the force exerted on the water, resulting in 0 resultant force and the object travels at a constant velocity.