3. Dynamics

Question 1

Define mass

Answer 1

Mass is the amount of matter in an object. Measured in kg.

Question 2

What is the property that resists the change in motion?

Answer 2

Mass
The greater the mass, the smaller the change produced by an applied force.

Question 3

Define weight.

Answer 3

Weight is force on an object caused by gravitational field acting on the mass. Measured in Newtons.

Question 4

How to calculate weight

Answer 4

weight=mass*accleration of freefall
w=mg
g=9.81 ms-2 or N kg-1

Question 5

Explain free fall

Answer 5

1. An object in free fall is falling solely under the influence of gravity
2. On Earth, all free-falling objects accelerate towards Earth at a rate of 9.81 m s−2
3. In the absence of air resistance, all bodies near the Earth fall with the same acceleration regardless of their mass

Question 6

How to calculate force

Answer 6

Force=massacceleration
resultant force= mass acceleration
acceleration will be in the same direction as this resultant force.

Question 7

What is newton’s first law of motion?

Answer 7

A body will remain at rest or move with constant velocity unless acted upon by a resultant force.

Question 8

What is newtons second law of motion?

Answer 8

A resultant force acting on a body will cause a change in momentum in the direction of the force. The rate of change in momentum is proportional to the magnitude of the force
This can also be written as F = ma where mass of the object is constant.

Question 9

What is newton’s third law of motion?

Answer 9

If body A exerts a force on body B, then body B will exert a force on body A of equal magnitude but in the opposite direction
Newton’s Third Law force pairs must act on different objects
Newton’s Third Law force pairs must also be of the same type e.g. gravitational or frictional

Question 10

Define linear momentum and how to calculate it.

Answer 10

Linear momentum is defined as the product of mass and velocity.
p=mv
SI unit for momentum= kg ms-1
because mass = kg
velocity= ms-1

Question 11

Define force. and how to calculate it.

Answer 11

Force is the rate of change of momentum on a body.
force= change in momentum/ change in time
change in momentum= final momentum- initial momentum

Question 12

Define drag forces and give examples.

Answer 12

Drag forces are forces acting the opposite directions to an object moving through a fluid. (gas or liquid)
examples- friction and air resistance
A key component of drag forces is that it increases with the speed of the object.

Question 13

1. When a car is accelerating what is the relationship between the driving force towards the right and frictional force towards the left?
2. When a car is moving with constant velocity what is the relationship between the driving force towards the right and frictional force towards the left?
3. When a car is decelerating what is the relationship between the driving force towards the right and frictional force towards the left?

NOTE- this is under the understanding of drag forces as drag forces increases as the speed of the object. eg- air resistance and friction.

Answer 13

1. driving force > frictional force
2. driving force = frictional force
3. frictional force > driving force

Question 14

Brief air resistance.

Answer 14

1. Air resistance is a drag force for objects moving in the air.
2. Air resistance depends on the shape of the body (object) and the speed it’s travelling.
3. Since drag force increases with speed, air resistance becomes important when objects move faster.

Question 15

Define terminal velocity .

Answer 15

definition- the maximum velocity reached by an object falling under gravity or accelerated by a constant force.

FOR understanding-
When the drag force is equal to the gravitational pull on the body, the body will no longer accelerate and will fall at a constant velocity
This is the maximum velocity that the object can have and is called the terminal velocity.

Question 16

What is the principal of conservation of momentum.

Answer 16

The total momentum of a system remains constant provided no external force acts on it.
For example if two objects collide:
the total momentum before the collision = the total momentum after the collision

Question 17

Define external forces

Answer 17

External forces are forces that act on a structure from outside e.g. friction and weight

Question 18

Define internal forces

Answer 18

Internal forces are forces exchanged by the particles in the system e.g. tension in a string

Question 19

Define elastic and inelastic collisions.

Answer 19

Elastic collisions are commonly those where objects colliding do not stick together and then move in opposite directions.
Inelastic collision are where objects collide and stick together after the collision.

If the kinetic energy is conserved, it is an elastic collision.
If the kinetic energy is not conserved, it is an inelastic collision.

Question 20

name the forces that-
1. two objects may attract each other because of the gravity of their masses
2. two objects may attract or repel each other because of their electric charges
3. two objects may touch
4. two objects may be attached by string and pull on each other
5. two objects may attract or repel each other due to magnetic fields

Answer 20

1. gravitational forces
2. electrical forces
3. contact forces
4. tension forces
5. magnetic forces

Question 21

what is upthrust?

Answer 21

Upthrust- any object placed in a fluid such as water or gas experiences an upwards force.