Define ‘resultant force’.

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

What happens if a resultant force acts on an object?

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

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

It can change…

- Speed
- Direction

How can the resultant force be found?

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

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.

Define friction.

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

Give an example of a frictional force.

Air resistance.

When work is done overcoming friction, what occurs?

Energy is dissipated, resulting in heating.

When does circular motion occur?

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

Describe the speed and velocity of an object in circular motion

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

Give an example of a force causing circular motion

Gravity, which causes the earth to orbit the sun.

State Hooke’s law

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

Give the equation for Hooke’s law

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

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

The limit of proportionality

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

Where the graph stops being linear.

What is a moment?

The rotational (or turning) effect of a force.

Give the equation for moments.

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

When does rotational equilibrium occur?

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

This is the principle of moments.

When is equilibrium reached?

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

What is a centre of mass?

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

What is a vector quantity?

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

What is a scalar quantity?

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- A quantity that has only magnitude, not direction.

Give examples of vectors

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- Velocity
- Force
- Acceleration
- Displacement

Give examples of scalars

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- Speed
- Direction

Describe how resultant forces can be represented visually

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

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