General Physics 1.5 Forces Flashcards

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1
Q

Define ‘resultant force’

A

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

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2
Q

What happens if a resultant force acts on an object?

A

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

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3
Q

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

A

It can change…
• Speed
• Direction

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4
Q

How can the resultant force be found?

A

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

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5
Q

What happens if there is zero resultant force?

A

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

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6
Q

Define friction.

A

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

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7
Q

Give an example of a frictional force.

A

Air resistance.

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8
Q

When work is done overcoming friction, what occurs?

A

Energy is dissipated, resulting in heating.

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9
Q

When does circular motion occur?

A

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

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10
Q

Describe the speed and velocity of an object in circular motion

A

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

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11
Q

Give an example of a force causing circular motion

A

Gravity, which causes the earth to orbit the sun.

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12
Q

State Hooke’s law

A

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

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13
Q

Give the equation for Hooke’s law

A

F=kx
Where…
F = force (N)
× = extension (m)
k = spring constant (N/m)

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14
Q

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

A

The limit of proportionality.

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15
Q

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

A

Where the graph stops being linear.

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16
Q

What is a moment?

A

The rotational (or turning) effect of a
force.

17
Q

Give the equation for moments.

A

moment (Nm) = force (N) x distance (m)
(note: distance is the perpendicular distance from the force to the pivot)

18
Q

When does rotational equilibrium occur?

A

When the sum of clockwise moments = the sum of anticlockwise moments
This is the principle of moments.

19
Q

When is equilibrium reached?

A

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

20
Q

What is a centre of mass?

A

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

21
Q

Describe how to find the centre of mass of a plane lamina.

A

• Suspend the object and a plumb line from the same point
• Trace the thread of the plumb line with a pencil
• Repeat using different points
• The centre of mass is where all the lines cross

22
Q

What is a vector quantity?

A

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

23
Q

What is a scalar quantity?

A

A quantity that has only magnitude, not direction.

24
Q

Give examples of vectors

A

• Velocity
• Force
• Acceleration
• Displacement

25
Q

Give examples of scalars

A

• Speed
• temp
Mass
Energy

26
Q

Describe how resultant forces can be represented visually

A

Use scale drawings of vector diagrams.
• Add force vectors tip to tail
• Connect them for the resultant force