Module 3 - Section 5 (Newtons laws, forces and momentum)

Question 1

What is a force?

Answer 1

A push or pull force that acts on an object due to the interaction with another object

Question 2

What are forces categorised under?

Answer 2

A vector
- direction and magnitude

Question 3

What are contact forces?

Answer 3

PHYSICALLY TOUCHING
-friction
-drag/air resistance
-tension
-thrust
-contact

Question 4

What are non-contact forces?

Answer 4

PHYSICALLY SEPERATED
-gravitational
-electrostatic
-magnetic

Question 5

How does forces come into play when a pen is dropped?

Answer 5

-A gravitational force acts on the mass of the pen causing it to accelerate towards the ground

Question 6

Whats the equation linking force acceleration and mass

Answer 6

F = m x a

Question 7

Whats the difference between mass and weight?

Answer 7

Mass is a physical property as in the amount of something (kg)

Weight is the downward force due to gravity acting on the mass (n)

Question 8

How do you find the centre of mass of an object?

Answer 8

MODELLING
Method:
-Cut out an irregular shape
-Cut 3 holes around the edge of the card
-hang the card through a nail on a clamp stand and draw on a straight line using weighted string
-hang the shape from the other holes repeating the same steps
-the place where the lines intercept is the centre of mass

NOTE: the centre of mass is not always on the shape.

Question 9

What does it mean when an object is in equilibrium?

Answer 9

The sum of the anti-clockwise moments = the sum of the clockwise moments

Question 10

What is the equation for moments?

Answer 10

Moment = force x distance from pivot

Question 11

What factors influence the drag force in a liquid?

Answer 11

SA
Velocity
Density of fluid

Question 12

How is terminal velocity changed?

Answer 12

SA: greater the SA = the greater the drag force so lower terminal velocity
Mass: greater mass = greater weight, so a larger drag force os required to equal the weight so a higher terminal velocity.

Question 13

What is density?

Answer 13

The mass per unit volume

Density = mass / volume

Question 14

What is the equation for pressure?

Answer 14

Pressure = Force / Area

Question 15

What is the rule about fluid pressure?

Answer 15

At a greater depth the pressure is larger

Question 16

How can the pressure in a fluid be calculated?

Answer 16

P = ⍴ h g

Pressure = density x depth x g (9.81)

Question 17

How can you derive the fluid pressure equation?

Answer 17

P = F/A

F = W = mg Therefore: P = mg/A

A = V/h Therefore: P = mgh/V

⍴ = m/V Therefore: P = ⍴hg

P = ⍴ h g

Question 18

When an object is floating in equilibrium what are the two things that are equal?

Answer 18

The upthrust and the weight

Question 19

What is Archimedes Principle?

Answer 19

The upthrust exerted on a body immersed in a fluid (whether fully or partially submerged) is equal to the weight of the fluid the body displaces.

Question 20

What is Newtons First law?

Answer 20

An object at constant velocity will remain at constant velocity until an external force acts on it.
It will remain at rest until a resultant force acts upon it (unbalanced)

Question 21

What is Newtons Second law?

Answer 21

F = ma

Acceleration is produces when a force acts on a mass and unbalances the forces.

Question 22

What is Newtons Third law?

Answer 22

Every action has an equal and opposite reaction force

• This MUST be the same size and same type of force acting in different directions.

Question 23

What is Momentum?

Answer 23

Momentum = mass x velocity

Question 24

What is the rule about momentum?

Answer 24

When objects collide the total momentum is conserved within the closed system as long as no external forces act on it.

Total momentum before = total momentum after

Question 25

What is a perfect elastic collision?

Answer 25

When there is no loss of kinetic energy eg: particle collisions

Question 26

What is an inelastic collision?

Answer 26

When kinetic energy is lost to other energy sources eg: sound and heat like car crashes.

Question 27

How would you calculate the change in momentum?

Answer 27

Momentum = Force x time