Topic 4 Dynamics - chapter 3

Question 1

which property of body resists change in motion?

Answer 1

mass

Question 2

what’s Newton’s second law of motion ?

Answer 2

for a body of constant mass, its acceleration is directly proportional to the resultant force applied to it.

F= ma
the greater the force, the greater the acceleration.

Question 3

what is the relationship between mass and acceleration of the object, if the resultant force remains constant?

Answer 3

the greater the mass, the smaller the acceleration.

the acceleration is inversely proportional to the mass.

Question 4

what is the center of the gravity?

Answer 4

the point where the object’s entire weight appears to act on.

Question 5

what is the weight of an object?

Answer 5

the weight on an object is a force caused by earth’s gravity.
w= mg where w= weight-N
m= mass-kg
g= gravitational field strength/
acceleration of free fall- ms^-2/ Nkg^-1

Question 6

which factor doesn’t affect the acceleration of the free fall?

Answer 6

the mass of the object doesn’t affect the acceleration of a falling object. however, air resistance may affect the acceleration of an object.

Question 7

what affects the air resistance of an object?

Answer 7

velocity and surface area of the object

Question 8

what is the gravitational field strength of the moon?

Answer 8

1.6 ms^-2

Question 9

what is the difference between mass and weight?

Answer 9

mass- doesn’t vary from place to place-kg

weight- this is a force- it depends on the strength of the gravity- N

Question 10

how does the gravitational strength of moon affects the force needed to move and lift an object?

Answer 10

it will be easier to lift things but not any easier to move things- this is because the mass remains same but the weight changes.

Question 11

what is inertia?

Answer 11

A property of matter by which it continues in its existing state of rest or uniform motion in a straight line, unless the state is changed by an external force.

Question 12

how is inertia different for different objects?

Answer 12

due to inertia, heavier objects are harder to move or change direction.

Question 13

what is the terminal velocity of a car?

Answer 13

the terminal velocity of a car is its maximum speed

Question 14

what are balanced forces?

Answer 14

when the resultant force is zero. the forces are said to be balanced.

Question 15

what are unbalanced forces?

Answer 15

when the object is accelerating/ when there is a resultant force, the forces are unbalanced.

Question 16

how do you calculate the resultant force?

Answer 16

add the forces acting along a straight line. take note of the relationship between the direction of the force and the sign of the force in the equation.

if the forces are acting along horizontal and vertical components, use vector addition to find the resultant force.

Question 17

describe the motion of a falling object.

Answer 17

the weight of the object will remain constant in a uniform gravitational field strength.

if the initial velocity of the object is 0 ms^-1,
the object will initially accelerate downwards as the magnitude of weight is more that air resistance.
as the object falls, the velocity increases. due to this, the air resistance increases and acceleration decreases.
the object will continue to accelerate to the point when the weight is equal to air resistance. this is called ‘terminal velocity’. now the velocity of the object will remain constant and the acceleration will be zero.

Question 18

how does air resistance affect a free falling object?

Answer 18

the air resistance will decrease the horizontal and vertical component of a projectile.
the terminal velocity will be reached earlier. (vertical)
and less horizontal distance will be travelled. (horizontal)

Question 19

what affects terminal velocity of an object?

Answer 19

terminal velocity of an object depends on the weight and surface area of the object.

Question 20

what is drag in fluids?

Answer 20

it is a resistive or viscous force which objects experience when they move through fluids-liquid or air
it is similar to friction.
it acts opposing to the direction of motion.
it can be reduce by giving the object a streamlined shape.
we rarely experience drag in air. this is because air is much less dense than water; its density is roughly 1/800 that of water. however, if you want to move faster, then drag is important.

the deeper the water gets, the more it resists.

Question 21

what are the types of forces?

Answer 21

pushes and pulls- make an object accelerate by pushing or pulling.
weight- force of gravity acting on the object.
friction- when two surface rub on one another; acts in opposite direction to the motion; always acts along a surface, never at an angle.
drag- resistant force in fluids.
upthrust- any object placed in fluids experiences an upward force.
contact force- normal reaction, perpendicular to the the surface which produces it.
tension- a force transmitted through a string, wire, cable or wire when it is pulled tight by forces acting from opposite ends; it is directed along the length of the wire and pulls equally on the object from the opposite end if the wire; it also acts on spring.

Question 22

how does contact force works?

Answer 22

when an object is on a surface/or another object, the surface becomes slightly compressed. its atoms are pushed slightly closer together and the interactive forces push back against the compressing force. the same happens with the object. therefore, two contact forces act in opposite in direction and are equal in magnitude.

Question 23

what is the upthrust force?

Answer 23

it can be thought of as the contact force of water on the object. it is caused by the pressure of the water pushing upwards on the object. pressure arises from the motion of the water molecules colliding with the boat and the net effect of all these forces is an upward force.

an object in an air has a very small upward force acting on it, because the density of the air around it is low.

Question 24

what are the characteristics of a Newton’s third law pair?

Answer 24

they act on different objects.
act in opposite direction.
are equal in magnitude.
are forces of the same type.