Unit 2: 2 - Forces

Question 0

What 2 features do forces always have?

Answer 0

Size and direction.

Question 1

What are forces measured in?

Answer 1

Newtons (N)

Question 2

What do forces always exert?

Answer 2

Equal and opposite forces. For example, if object A (a car) hits object B (let’s say, a barrier), object A exerts force onto B and B exerts an equal force but in the opposite direction into A.

Question 3

In what direction does the force of weight always act?

Answer 3

Downwards, due to gravity.

Question 4

What is resultant force?

Answer 4

As most objects have more than one force acting on them at any one time, the resultant force is the single force that would have the same effect on the object as all the original forces acting together. For example, 2 forces of 3N and 4N would make a resultant force of 7N.

Question 5

What happens when the resultant force on an object is 0?

Answer 5

• If the object is at rest, it remains at rest.

- If the object is moving, it will carry on moving at the same speed in the same direction.

Question 6

What happens when the resultant force is not 0?

Answer 6

• If the object is at rest, it will accelerate in the direction of the force.
• If the object is moving in the same direction of the resultant force, it will accelerate in that direction.
• If the object is moving in the opposite direction, it will decelerate.

Question 7

How do we find the resultant force of an object?

Answer 7

F = m*a
Where F is the resultant force (N),
m is the mass (kg),
And a is the acceleration (m/s^2).

Question 8

If a vehicle is driving at a steady speed, what is it’s resultant force?

Answer 8

0. The driving forces are equal and opposite to the frictional forces so the vehicle does not accelerate nor decelerate.

Question 9

What are the 3 key stopping terms on the road?

Answer 9

• Stopping distance (thinking distance + braking distance)
• Thinking distance (increased if driver is drunk or under the influence of drugs)
• Braking distance (increased by bad weather, worn brakes/tyres and bad roads)

Question 10

What is the acceleration due to gravity on Earth?

Answer 10

9.8m/s^2

Question 11

How do we find the weight in Newtons?

Answer 11

Weight in N (W) = Mass in kg (m) * Acceleration due to gravity (m/s^2) (9.8m/s/s on Earth)

Question 12

What force is generated when an object falls through a fluid?

Answer 12

Drag force. The faster the object moves, the bigger the drag force becomes.

Question 13

What happens when the drag force becomes big enough to equal the weight of the object?

Answer 13

The resultant force becomes 0 as the object stops accelerating.

Question 14

What is this largest stable velocity called?

Answer 14

Terminal velocity.

Question 15

What is the increase in length of a spring called?

Answer 15

Stretching

Question 16

Objects that stretch because a force is applied and revert back to their original form are…

Answer 16

Elastic

Question 17

The opposite of elastic is…

Answer 17

Inelastic

Question 18

What type of graph line is drawn from an elastic spring?

Answer 18

Directly proportional

Question 19

What is the term used when the spring pulls too much that it does not return back?

Answer 19

Limit of proportionality

Question 20

What is Hooke’s Law?

Answer 20

Force (N) = spring constant of the spring (N/m) * Extension (m)
F=k*e

Question 21

A spring has a constant of 30N/m. If the extension is 0.3m,what is the force applied? (Hooke’s law)

Answer 21

F=ke
Force = 300.3
Force = 9N

Question 22

How can you tell if a spring has reached its limit of proportionality?

Answer 22

Its graph line will steepen by an unusual amount, which is not proportional to the rest of the graph.