Topic 9 Flashcards by Daniel Barrett

Whats a moment ?

A moment is the turning effect of a force around a fixed point

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Whats the equation for moment ?

Moment=Force × perpendicular distance from pivot

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What are the units of moment ?

The units of moment are N/m

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What is the unit of force ?

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Where is a turning effect larger?

As far away from the pivot as possible

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How is moment calculated ?

The Moment (measured in Nm) is equal to the Force (measured in Newtons) multiplied by the perpendicular distance from pivot (measured in metres)

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If a force of 5N is applied 6m from the pivot, what is the moment about the pivot?

30 N/m

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For an object moving in a circular motion to be in equilibrium what has to happen ?

The sum of the clockwise moments must be equal to the sum of the anti-clockwise moments acting on the object.

This means that the object is not rotating or rotates at a constant speed.

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For an object moving In linear motion to be in equilibrium what has to happen ?

There must be no resultant force acting on the object.

It must be stationary or travelling at a constant speed in a straight line.

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Explain what levers and gears do

We use levers and gears to transmit (send) the rotational effect of a force from one place to another.
We can use levers to increase the distance between the pivot and where we’re applying the force.
Moment = force x distance, so using a lever means we need to use less force to get the same moment.

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What do we use levers and gears to transmit ?

We use levers and gears to transmit (send) the rotational effect of a force from one place to another.

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What are gears ?

Gears are circular discs with ‘teeth’ around their edges.

Their teeth interlock. So if we turn one gear, another turns in the opposite direction.

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Gears are circular discs with ‘teeth’ around their edges and their teeth interlock.
So if we turn one gear what happens to another ?

So if we turn one gear, another turns in the opposite direction.

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What can a set of gears do ?

A set of gears can transmit (send) the rotational effect of a force from one place to another.

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What can we use to change the moment of the forc ?

We can use different sized gears to change the moment of the force.

For example, if we send a force to a larger gear, there will be a bigger moment.

This is because the distance to the pivot is greater.

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What is the name for circular disks with interlocking teeth, used to transmit rotational effects?

Gears

Whats a force ?

A force is a push or pull that acts on an object when it interacts with another object.

What are the two types of forces .

Contact force

Nom-contact force

When does a non contact force happen ?

Non-contact forces happen when objects are separated (not touching).

What are examples of non contact forces ?

Gravitational force, electrostatic force and magnetic force are all examples of non-contact forces.

When do contact forces happen ?

Contact forces happen when two objects are physically touching.

What are examples of contact forces ?

Friction, air resistance, tension and normal contact force are all examples of contact forces.

What is an interaction pair ?

An interaction pair is a set of 2 forces that are equal and opposite, acting on 2 interacting objects.

When does the contact force, air resistance come about ?

Air resistance comes about when an object moves through air and collides with (hits) air molecules.

This create a force that slows the object down.

When does the contact force, Normal contact force come about ?

When you push on a table, your hand doesn't move through it. This is because the normal contact force from the table pushes equally on your hand.

When does the contact force, Friction come about ?

Friction comes about whenever two surfaces are touching and try to move against each other. Tiny bumps in the surface interlock (overlap or fit together). This creates a frictional force that opposes their motion.

When does the contact force, tension come about ?

Tension is the pulling force that a string or cable exerts (creates) when something or someone pulls on it.

What does friction do ?

Friction opposes motion and often causes heating.

How can you reduce friction ?

Separating two surfaces with a thin layer of oil can reduce friction and allow them to move more freely across each other. Fidget spinners reduce friction to the lowest level possible to let them spin for as long as possible.

How is air resistance a frictional force .

Air resistance is a frictional force. Air resistance opposes an object's motion.

What is a diagram showing the forces acting on an object ?

A free body force diagram

What are the acting on a driving car ?

The forces acting on a driving car are the driving force, the normal contact force, the weight and friction.

What are the forces acting on a skydiver ?

The forces acting on a skydiver are air resistance (acting upwards) and the skydiver’s weight (acting downwards).

What can we use to work out the resultant force when more than one force is acting on an object ?

We can use free body diagrams to work out the resultant force when more than one force is acting on an object.

What can we use to see if an objects resultant force is in equilibrium ?

We can also use the diagrams to see if an object is in equilibrium. If the resultant force is zero, we say the object is in equilibrium.

If the resultant force is zero, what can we say ?

If the resultant force is zero, we say the object is in equilibrium.

Work out the resulatant for es for an accelerating car when : The force acting downwards is 5000N and upwards is 5000N. The force acting forwards is 3000N and backwards 1000N.

Resultant force upwards = 5000 N - 5000 N = 0 N Resultant force forwards = 3000 N - 1000 N = 2000 N

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Fact

``` We can split a force into horizontal and vertical parts. We can use grid lines to find the size of these forces. A force is drawn in the diagram above. It can be split into two forces: 3N vertically (upwards) and 4N horizontally (sideways). ```