Topic 1.5 - Forces Flashcards Preview

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Flashcards in Topic 1.5 - Forces Deck (26)
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1

Define ‘resultant force’.

The sum of all the individual forces acting on an object (taking directions into account).

2

What happens if a resultant force acts on an object?

It causes a change of momentum in the direction of the force.

3

How can a resultant force change the motion of an object?

It can change…

  • Speed
  • Direction

4

How can the resultant force be found?

Adding force vectors together, tip (arrow) to tail.

5

What happens if there is zero resultant force?

The object will remain stationary, or (if moving) will continue to move in the same direction with the same speed.

6

Define friction.

Friction is the force providing resistance to the motion of two surfaces sliding past each other.

7

Give an example of a frictional force.

Air resistance.

8

When work is done overcoming friction, what occurs?

Energy is dissipated, resulting in heating.

9

When does circular motion occur?

When a force is acting perpendicular to the motion of an object.

10

Describe the speed and velocity of an object in circular motion

  • The speed is constant
  • The velocity is always changing, since it is constantly changing direction

11

Give an example of a force causing circular motion

Gravity, which causes the earth to orbit the sun.

12

State Hooke’s law

The force on an object (eg. a wire or spring) is directly proportional to its extension.

13

Give the equation for Hooke’s law

F = kx Where... F = force (N) x = extension (m) k = spring constant (N/m)

14

At what point does Hooke’s law no longer apply?

The limit of proportionality

15

What does the limit of proportionality look like on an extension-load graph?

Where the graph stops being linear.

16

What is a moment?

The rotational (or turning) effect of a force.

17

Give the equation for moments.

moment (Nm) = force (N) x distance (m)

18

When does rotational equilibrium occur?

When the sum of clockwise moments = the sum of anticlockwise moments

This is the principle of moments.

19

When is equilibrium reached?

When there is no resultant force or turning effect. (clockwise = anticlockwise moments)

20

What is a centre of mass?

A single point through which the force of an object’s weight acts. (This is a modelling assumption).

21

What is a vector quantity?

  • A vector quantity has both magnitude (size) and direction.

22

What is a scalar quantity?

  • A quantity that has only magnitude, not direction.

23

Give examples of vectors

  • Velocity
  • Force
  • Acceleration
  • Displacement

24

Give examples of scalars

  • Speed
  • Direction

25

Describe how resultant forces can be represented visually

  • Add force vectors tip to tail
  • Connect them for the resultant force

26

Draw an extension load graph and idenitfy when hooke's law stops being obeyed