Forces and their interactions (5.1) (M)

Question 1

Define a scalar quantity

Answer 1

a quantity that magnitude (size) only

Question 2

Define a vector quantity

Answer 2

a quantity that has magnitude (size) and an associated direction

Question 3

How may a vector quantity be represented

Answer 3

A vector quantity may be represented by an arrow.

The length of the arrow represents the magnitude, and the direction of the arrow the direction of the vector quantity

note: the size/length of an arrow will represent the force e.g. 100N = 10cm, 250N = 25cm i.e. must be scale-drawings

Question 4

Define a force

Answer 4

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

Question 5

What are the two types of forces between objects?

Answer 5

contact and non-contact forces

Question 6

What is a contact force?

Answer 6

when the objects are physically touching

Question 7

What is a non-contact force?

Answer 7

when the objects are physically separated

Question 8

4 needed

What are examples of contact forces?

Answer 8

• friction
• air resistance
• tension
• normal contact force (i.e. object lying on surface)

Question 9

3 needed

What are examples of non-contact forces?

Answer 9

• gravitational force
• electrostatic force
• magnetic force

anything with a field is a non-contact force

Question 10

Force is a (…) quantity

Answer 10

vector

Question 11

How would you describe the forces in an object sliding down a slope?

Answer 11

Two objects sliding past each other experience friction forces.

Question 12

What is weight?

Answer 12

the force acting on an object due to gravity

Question 13

What is the force of gravity close to the Earth is due to?

Answer 13

the gravitational field around the Earth

Question 14

What does the weight of an object depend on?

Answer 14

the gravitational field strength at the point where the object is

and mass of object

Question 15

The weight of an object may be considered to act at a single point. What is this referred to as?

Answer 15

the centre of mass

Question 16

What is the centre of mass?

Answer 16

the single point at which the weight of an object may be considered to act

Question 17

Describe the relationship between the weight and mass of an object

Answer 17

directly proportional

Question 18

How is weight measured?

Answer 18

using a calibrated spring-balance (a newtonmeter)

Question 19

What is the resultant force?

Answer 19

A single force that has the same effect as all the original forces combined (acting together)

• A number of forces acting on an object may be replaced by a single force*
• e.g. 100N to the right and 60N to the left, may be replaced by a resultant force of 40N to the right*

Question 20

A force (thrust) is acting 100N to the right of the car, making it move, air resistance is creating a force of 20N to the left and friction a force of 10N to the left. Describe what happens?

Answer 20

A resultant force of 70N acts to the right, making the car accelerate

Question 21

4 marks

How do you describe it when opposite forces are equal?

Answer 21

The forces are balanced. It is in equilibrium. The resultant force is 0. The object will not move.

Question 22

Describe resolution of forces (resolving forces)

Answer 22

A single force that can be resolved into two components acting at right angles to each other.

Question 23

In resolution of forces (ie. resolving forces), the two component forces together have the (…) effect as the single force

Answer 23

same

Question 24

Draw a vector diagram to illustrate a resolution of forces (resolving force) from a single force of 5N at 37^oC

Answer 24

only can know length of horizontal/vertical component once drawn and measured with ruler

Question 25

# 4 points A rectangular block on a wooden board is placed on its side, how all this affect the stability if the block?

Answer 25

* stability will increase * centre of mass is lower * base is wider * block will have to be tilted to greater angle

Question 26

Draw a vector diagram to show a force of 61N and a force of 40N acting at right angles to each other

Answer 26

Question 27

# 2 marks Why coulda sled being pulled at an angle to the surface mean that the value calculated for the constant of friction would not be appropriate?

Answer 27

only (the horizontal) component of the force would be pulling the sled forward the vertical component of the force lifts the sled reducing the force of the surface on the sled

Question 28

What is the problem with changing 2 variables?

Answer 28

it is not possible to know the effect of each variable