forces

What is a force And what can the change on an object

A push or pull act on an object caused by interacting with something - they can change an objects

• speed

• Direction

• Shape

explain why during races the speed changes

• at start of race the acceleration increases so speed increases

• road is not flat so speed decreases when going uphill

• if competitor goes round a bend speed decreases

• may tire towards end so force they exert decreases which decreases speed

• resistive forces may increases causing speed to decrease

What is a scalar quantity

A quantity that only has magnitude and isnt direction dependent (measurements with numbers and units)

Give scalar quantities examples

Temperature, density, speed, distance, mass

how to determine how changing the force effects acceleration with a trolley

1. mark start and end point in table and measure the distance between them with metre rule

2. clamp a pulley onto end of desk

3. starch a string to trolley and over to the pulley leaving some string end loose

4. attach a weight stack onto end of string

5. hold car and add a weight stack of 1N

6. start timer and record how long it took to reach end

7. repeat with decreasing masses

what to do if the weight of the mass is unknown

use equation W=mg

what is a closed system

• when resultant force acting on system (object) is zero and energy remains constant

What are vector quantities

A quantity that has both magnitude and direction (20m/s upwards)

why does

Examples of vector quantities

• displacement, acceleration, force velocity

Wht is the difference between speed and velocity

Speed is how FAST an objects is moving eg 20 m/s

• velocity is the speeed in a given direction - eg: 20m/s north

What is the difference between displacement and direction

Displacement is the OVERALL change of a position from start to finish

Direction tells which way something is moving

What are vectors represented by and what does it show

As an arrow

• length shows magnitude of force

• Way its pointing shows direction of force

What are the two categories forces can be split into

1. Contact forces: when forces are touching or colliding

2. Non-contact: objects dont need to be touching to exert a force

Give three examples of contact forces

• friction

• Air / water resistance

• Tension

In terms of forces if tyres are faulty how can this effect breaking distance

• due to less grip on word, less frictional forces acting against tires so driving forces of tire will be larger so resultant force larger in forward direction

• So larger force required to break

Give three examples of a non-contact force

1. Gravitational forces

2. Electrostatic forces

3. Magnetic forces

Is force a scaler of vector quantity

Vector as it as magnitude (size) nd direction

What can magnetic and charged objects be

Attractive or a repulsive force

What is drag

Fraction or an air/water resistance force

What is upthrust

Force from water

What is thrust

ALWAYS a forward force - in direction of motion

What is weight

The force that acts on an object due to the pull of gravity and the objects mass (pulls something down)

What does weight depend on

• gravitational field strength

• objects mass

• On different planets weight changes due to having different gravitational field strength

Wat is unit used for weight

Newtons

What i mass

The amount of stuff in an object which NEVER changes - kg

What is the centre of mass

The force acting on an object from a point where whole mass is concentrated

How to find centre of mass of an regular object (Has same density)

Will be in centre of object

How to find centre of mass

• make a whole in material

• Plumb line suspended from same point as hole and draw line with a ruler

• Repeat with making a whole at different point

• Where the lines cross = centre of mass

What is the relationship with mass and weight

They are directly proportional so if you double mass, weight doubles

What can be used to measure an objects weight

Calibrated spring balance or newton meter

What is gravity

The force that attracts all masses which makes everything move towards the mass

What is th name given to the force that is equivalent to all the other forces acting on the object

Resultant force - find it by taking away both vertical directions from achother and both horizontal directions from each other

What is meant by when a force does work

Energy has been transferred causing object to be displaced through a distance

What is equation to calculate work done, give units

Work done (J) = force (N) x distance (metres)

What distance must be used when calculating work

The distance that the object moved along the line action of force

Under what circumstance is 1 oule of work done

When a force of 1 N causes a displacement of 1 metre

How many newton metres are equivalent to 1 joule of energy

1 Nm

What occurs when work is done against frictional forces

• rise in temperature of object

• Kinetic energy converted to heat

Why does ir resistance cause an object to slow down

• object does work against air resistance

• Kinetic energy is converted to heat, slowing down the object

What happens when a force moves on an object

Energy is transferred/work is done

What happens when a force dos work

Energy is transferred from one store to another but also some energy is dissipated to thermal through friction

What is power

The rate at which energy is transferred

What is hookes law

The extension is directly proportional to the force applied, provided limit of proportionality is not exceeded

Explain why there must be two forces applied to an object to change an objects shape

• a stationary object s internal forces will be at equilibrium (forces balance so won’t move) so n deformation

• More than one force must be applied in opposite directions to overcome internal forces

When u apply a force to an object what may happen - what must happen due to this

May cause it to bend, stretch, compress - must be more than one force acting on object otherwise object will not change shape but move in direction of force

Equation linking force and extension

F= k(n/m) x e ( m)

What is inelastic deformation (plastic)

A deformation which exults in object to be permanently stretched and doesnt originate back to original shape when force is removed

What happens when something decompresses (after spring has been pressed down on)

During compression the elastic potential energy increases

• when decompresses it decreases

Describe in terms of forces and energy what happens when a gymnast jumps on trampoline pad

• When jumps on trampoline she applies maximum force of her weight onto trampoline causing spring to conoress so work is done and elastic potential energy increases if trampoline and decreases in girl

• When decompresses (spring springs back) ep energy decreases and ke increases of girl as spring will exert a force on girl

What is elastic deformation

When a force is applied on an object and it can return to original shape

What happens if an object is elastically deformed

All energy transferred to elastic store

What type of energy is tired in a n object once stretched

Elastic potential energy

What can extension b replaced with in equation of for spring force

Compression

If there is a higher extension of spring what does this mean

Then it is more stretchy (if exceeds limit it is too stretchy so hit floor)

How does an elastic object overeach limit of proportionalality

If exceeds elastic potential energy

What does it mean if an object has a higher spring constant

It is a stiffer material so requires more force to stretch it

How to get extension

extended length - original

What happens when limit of proportionality is exceeded

Object will behave plastically (remain in deformed shape)

Resolving resultant forces- what must all arrows of forces be when drawing a diagram

Tip to tail

How to find resultant force

1. Find scale u would use eg: 1N=2cm

2. Draw forces named

3. Connect unknown force with line and measure with ruler

4. Convert cm into N

How to find other forces if given resultant force

• find scale u will use

• Draw resultant force (diagonal line) in cm

• Measure with ruler the other forces

• Convert to newtons

What is speed

Tells us how fast an object is travelling

• distance divide by time

What is a cars speed

What isa cyclist speed

What is a planes speed

25m/s

• 6m/s

• 250m/s

What is a speed of walking

What is speed of running

What is speed of a train

• 1.5m/s

• 3m/s

• 30m/s

What do curves represent on graphs

Acceleration / deceleration (speeding up or slowing down )

What does it mean if a force is said to do work

Force causes object to be displaced through a distance

What is equation for work done

Work (joules) = force (N) xx distance

What happens when work is done against fractional forces

• object rises in temperature

• Kinetic energy is converted to heat

How does air restance slow an object down

• the object will do work against air resistance force

• Kinetic energy in then converted the thermal energy slowing down the object

Typical value for speed of sound

330m/s

Why can an object travelling at a constant speed in a circle not have a constant velocity

• Speed is a scalar quantity

• Velocity is a vector which means it can only have a constant if direction is constant

• In a circular motion direction is not constant as it is constantly changing

What is the value of acceleration of an object in free fall near earths surface

9.8m/s squared

What is Newton’s first law

A resultant force is required to change the motion of an object

Using Newton’s first law, if all forces are balanced on a stationary object

• result force will equal zero as driving forces are balanced

• so object will remain at stationary

• as a non zero resultant force is needed to change an objects velocity

if a zero resultant force is applied to an object moving at a constant speed what happens

• all forces are balanced so resultant force is zero

• So object will move at constant velocity

• As non zero resultant force needed to change velocity

If the resultant force is zero and an object is moving what happens to its motion

Remain moving at a constant speed as resultant force is zero

What is a resultant force

The overall force acting on object when two forces are combined which results in objects motion (resistant force and driving force)

• subtract vertical and horizontal forces to get its motion

If driving forces aren’t balanced what does this mean

That the resultant force is unbalanced so it will cause object to accelerate or decelerate

What does an objects acceleration depend on when a force is applied

Its initial motion

• if stationary

• If moving left/rght

• Speed which it travels at

• If it changes direction

If a object is stationary and the resultant force is is right direction what heppens

Moves to right

If object is moving right and direction of resultant force is right what happens

Object seeds up

If object is moving left and resultant force is moving right what happens

Objects speed slows down / decelerates

If object is travelling at a slow speed and resultant force acts in backwards direction what happens

Object stops moving

What is newtons 2nd law

If a non-zero resultant force is applied it causes object to accelerate

• the acceleration of object is directly proportional to resultant force size (larger force larger speed)

• The acceleration is inversely proportional to the mass of the object (if same force applied to an object with a larger mass acceleration would e lower than smaller mass object) - more inertia needed

From Newton’s second law what is the relationship with acceleration and mass

• they are inversely proportional

• so if an object has a large inertial mass this means a larger force is needed to be applied to cause an object to accelerate for the same force applied to an object with smaller inertial mass

How to find inertial mass

F (resultant force) = m (mass) x acceleration

What is inertia

A measure of how difficult it is to change an objects velocity

What is Newton’s third law

when two forces interact, they exert equal but opposite forces v

How to find Resultat force

F = mass (kg) x acceleration

What is unit for acceleration

M/s squared

What is inertia

The tendency (likelihood) for an object to resist changes in its motion

• Mens how difficult it is to change an objects velocity

If an a person weights 40kg and the other weighs 80kg what does this mean in terms of inertia

• 80kg person requires more inerta as a larger force is needed to change persons velocity so will stay at rest until a large force acts upon it

What is newtons 3rd law

When two forces interact the orcas will be equal an opposite

when a submerine submerges into water why does pressure increase

• height of water above submerine increases

• which increases weight force of water acting on submerine

• so pressure increases

Using newtons law, why is a seatbelt needed

• because when a care suddenly stops a force is applied onto the car but not the person l

• Person will continue moving in forward direction unless a force acts upon person

• So the seatbelt provides a larger resultant force to bodys forward force force which when person moves forward it stops persons motion moving forward and person accelerates backwards

What can be said about resistant and driving forces when car s travelling at a constant velocity

The resistant and driving forces will balance and equal one another

If an object changes direction but at a constant speed is there a resultant force

Since there is a change in direction there is a change in velocity so there must be a resultant force

For an object to accelerate what must it have

Small mass or larger force