# P5:Forces Flashcards

What do vector quantities have

•Magnitude •Direction

Physical quantities of vectors include …

•force•velocity•displacement•acceleration•momentum

What is a scalar quantity

A physical quantity that only contains magnitude and NOT DIRECTION

Scalar quantities include…

•Speed•Distance •Mass•Temperature •Time

What usually represents a vector, and what does this symbol show

Usually represented by an arrow •length of arrow represents magnitude •direction of arrow represents the direction of the quantity

Forces can be…

•contact (when to objects have to be touching for a force to act) E.G:friction, air resistance OR•non-contact (when an object doesn’t need to be touching for a force to act) E.G:magnetic force, gravitational force

A force is a…

Push or pull on an object that is caused by it interacting with something

When two objects interact…

There is a force produced on both sides

Define the term ‘interaction pair’

A pair of forces that are equal and opposite and act on two interacting objects

Gravitational force is…

The force of attraction between masses

What are gravity’s two main important effects

•on the surface of the planet, it makes all things fall towards the ground AND•it gives everything a weight

Define the term ‘mass’

The amount of of ‘stuff’ in an object

What is weight

Weight is the force acting on an object due to gravity.Close to the earth, this force is caused by the gravitational field around the eating

Gravitational field strength varies, where is it strongest

It’s stronger the closer you are to the mass and it’s stronger for larger masses

What does the weight of an object depend on?

The strength of a gravitational force at the location of the object. This means the weight of an object changes with location

Weight is measured in …

Newtons

What is the term to describe the weight force acting from a single point on an object

‘Centre of mass’

Weight is measured using…

A calibrated spring balance or newtonmeter

Mass and weight are directly proportional. What equation would you use to work out the weight of an object?

Weight(N)=Mass(KG) x Gravitational Field Strength(N/KG)

Increasing the mass of an object increases his weight. Write this using the direct proportional symbol

W ∝ M

What can you use to show the forces acting on an object

A free body diagram

What do the things on a free body diagram represent

•The size of the arrows show the relative magnitudes of the forces •The direction show the direction of forces acting on the object

A resultant force is…

The overall force on a point or object

How many forces act on an object along any direction

At least two

If you have a number of forces acting at a singles point what can you replace them with

A single force AKA: the resultant force

If the forces all act along a parallel line, how is the overall effect found …

By adding those going in the same direction and subtracting any force going in the opposite direction

If w resultant force moves an object through a distance…

Energy is transferred & work is done

To make something move…

A force must be applied

The thing applying the force needs…

A source of energy E.G:food or fuel

Work is done even if the energy transferred is …

Useful or wasted

Equation for work done

Work Done(J)=Force(N) x Distance(m) W=FxS

One joule of work is done when a force of…

One newton caused an object to move a distance of one metre.

Conversion of joules to newton meters

1J = 1Nm

How to use a scale drawing to find a resultant force

1.Draw all the forces acting on an object, to scale ‘tip-to-tail’2.Draw a straight line from the start of the first force to the end of the last force (resultant force)3.Measure length of resultant force on the diagram to find the magnitude, angle and direction of the force

If all the forces acting on an object combine to give a resultant force of zero Or If the forces are balanced

The object is at an equilibrium

For three forces the scale diagram should…

Form a triangle

To draw an equilibrium the tip of the last force…

Should end where the tail of the first force you drew began

If told to find the missing force when an object is at equilibrium, you should

•draw out the forces you do know•join the end of the last force to the start of the first force•^ this line is the missing force so you can measure its size and direction

Not all forces act…

Horizontally or vertically, some are at awkward angles

If you find a force with an awkward angle…

•split it into two components at right angles (acting together these components have the same effect as the single force)

To resolve an single force…

•split it into components by drawing it on a grid •draw the force to scale•add horizontal and vertical components along grid lines •Then measure the components

When you apply a force to an object you may cause it to…

Stretch, compress or bend ^these actions transfer energy

If an object is being stretched, compressed or bent you need…

More than one force acting on the object otherwise the object would simply move in the direction of the applied force

An object has been elastically deformed if…

It can go back to its original shape and length after the force has been removed. They are called elastic objects E.G: a spring

An object has been inelastically deformed if…

It doesn’t return to its original shape and length after the force has been removed

Work is done when a forced stretches or compressed an object because…

Energy is transferred to the elastic potential energy store of the object

If work is done in an elastically deformed object…

ALL energy is transferred to the objects elastic potential energy store

Extension is directly proportionately to force

F ∝ e This is the equation:F(N)=K(N/m) x e(m)

The spring constant depends on…

The material that you are stretching•a stiffer spring has a greater spring constant

The F=Ke equation also works for compression…

Where e is just the difference between the natural and compressed lengths (The compression)

There is a limit to the amount of force you can apply to an object…

To keep on increasing it proportionally

Distance is just how far an object has moved its has…

A scalar quantity

Displacement measures the distance and direction in w straight line from an objects starting point to its finishing point

It is a vector quantity E.G: a bearing

EXAMPLE:If you walk 5m north and 5m south…

Your displacement is 0 But the distance travelled is 10m

Speed and velocity both measure how fast you’re going, but…

•Speed is a scalar quantity •velocity is a vector quantity