science exam sem 2 year 10 physics, energy, and a bit of chemistry

what is scalar

a physical quantity described by size

what is vector

a physical quantity described by a size and direction

what is distance

total length of a given path travelled between two points, scalar quantity. usually measured in metres

what is displacement

straight-line distance and direction between the start and finish of a motion, vector quantity. usually measured in metres

what is speed

rate of change of distance over time, scalar. usually measured in metres per second

what is velocity

rate of change of displacement over time, vector. usually measured in metres per second

explain the difference between distance and displacement

distances the total amount travelled and displacement is how far away the object is from it’s starting point

explain the difference between speed and velocity

speed has no direction and is a scalar quantity.

velocity has direction and is a vector quantity 

what’s the formula for speed and velocity, (use triangle)

(d = distance for speed and displacement for velocity)

so d is on top, then bottom left is Vav(average velocity or speed) then bottom right is time

what is acceleration

change in velocity over time, usually measured in m/s² 

what is acceleration due to gravity

objects have a downwards acceleration due to a planet’s gravitational field. g is the symbol for it. on earth, g ≈ 9.8m/s² at sea lvl

what does v and u mean

v is final velocity and u is initial velocity

what’s the formula for calculating acceleration (use triangle)

change in velocity on top, a acceleration on bottom left, and change in time on bottom right

The Greek letter ∆ means

change

what can happen when a force is applied to an object

• start moving

• stop moving

• speed up

• slow down

• change direction

• change shape

• start/stop spinning

what is force

• a push or a pull

• can change an object’s motion

• symbol is F and is measured in N(newtons)

• not required to keep an object moving, friction slows it down

• vector quantities

what is net force

resultant force from the addition or subtraction of forces

how to calculate net force

• Fnet​=m×a

• If there’s more than one force, find the difference (biggest minus smallest)

• The direction is always that of the larger force

what is inertia

a property of matter by which it continues in its existing state of uniform motion unless acted on by an external force

what’s newtons first law of motion

• law of inertia

• an object will remain at rest or in constant motion in a. straight line unless acted on by a net unbalanced force

explain how seatbelts work using Newton’s first law of motion

1. describe motion before change: if a car is travelling 100km/h, so are the passengers

2. describe motion during change: when car suddenly stops, a force is exerted on the car, but not passengers. the passengers will continue moving 100km/h

3. explain how/why the motion of the object changes: if the passengers r wearing seatbelts, the seatbelts will exert a force to stop the passenger

what is newton’s second law

• an object will accelerate in the direction of an unbalanced force acting on it

• acceleration depends on mass and size of net force 

• we can write the law as: F = m x a 

• force and acceleration r both vector quantities, and will act in the same direction

how to calculate newtons second law triangle

Fnet(net force) on top, m (mass) on left, a(acceleration) on right 

what’s newtons third law

• for every action, there’s an equal and opposite reaction on the other object

• action-reaction pairs act on different objects, so do not cancel each other out

• the reaction force will be equal in size, but opposite in direction to the action force

• e.g. when u step forward, pushing back on the ground gives a reaction force of the ground pushing forward on us, without friction the foot will just slide and you won’t move forward

when asked to describe a situation using newtons third law of motion, you need to:

• state the direction of the action force

• state the direction of the reaction force

explain how a fish is able to swim through water using newtons third law of motion

the fish’s fins push backwards against the water, the water pushes forwards against the fish with the same force

are products formed every time molecules of reactants collide

not necessarily, molecules must collide with enough energy and with the correct alignment

how can the rate of a chemical reaction be slowed down

• reduce the surface area of particles reacting

• reduce the concentration of the reactants

• reduce the temperature of the reactants

why does increasing the surface area increase the rate of reaction

• increases the number of molecules exposed to other reactant

• increases number of collisions

• increases likelihood of successful collisions

why does diluting a solution decrease the rate of reaction

• diluting reduces concentration, so reduces number of molecules in the same volume

• less particles means less collisions

• less chance of successful collisions, so slower reaction rate

define momentum

the product of mass and velocity, usually measured in kg m/s. all moving objects possess momentum. momentum is passed from one object to another in a collision

what’s the formula for momentum using triangle

p(momentum) on top, m(mass) on left, v(velocity) on right

what’s the law of conservation of momentum

• in an isolate system, the total momentum does not change in a collision, this means the initial momentum is equal to the final momentum

what is a synthesis reaction

a + b → ab

what is a decomposition reaction

ab → a + b

what is an acid and base reaction

acid + base (metal hydroxide) → water + metal salt

what is an acid and metal reaction

acid + metal → salt + hydrogen

what is an acid and metal oxide

acid + metal oxide → salt + water

what is an acid and metal carbonate

acid + metal carbonate → salt + water + carbon dioxide

what is a displacement-time graph

• the displacement of an object (vertical axis)

• depends on the time taken for the motion (horizontal axis)

• the gradient shows the velocity (measured in m/s)

• a straight line indicates a constant velocity

• a flat line represents a velocity of 0m/s; the object is stationary

what does this show

the objects motion is moving forward (positive direction) at a constant speed

what does this show

the object is moving in the negative direction at a constant speed

what does this show

the first third is speeding up from rest, 2nd third shows its going the fastest speed, and last third is slowing down to rest

what does this show

the object is moving away, then returning to the starting point

what does a velocity-time graph show

• shows how the velocity of an object (vertical axis) depends on the time taken for the motion (horizontal axis)

• the gradient shows the acceleration (measured in m/s²)

• a straight line indicates a constant acceleration

• a flat liner represents a constant velocity

• the shaded area under the graph represents the displacement (measured in m)

what does this mean

the objects motion is moving forward from rest in a. positive direction with a constant increase of speed

what does this mean

the object is speeding up from rest in 1/3, 2/3 the object has the greatest acceleration, and 3/3 there is a constant speed

what does this mean

the object is moving forward to stop (positive direction) with a constant decrease of speed

what does this show

the object is starting, speeding up, then slowing down to a stop

what is potential energy

• the energy something has because of its position or height or stored condition — not because it’s moving.

• its stored energy that has the potential to do work

• stored in objects, which can have more than one type of potential energy depending on their position or strucutre 

what r some types of potential energy and explain

1. gravitational: energy stored when something is stored above the ground

2. chemical: energy stored in chemical bonds

3. elastic: energy stored when something is stretched or compressed

4. electrical: energy stored due to charged particles being separated

5. nuclear: energy stored within the nucleus of an atom

6. magnetic: energy stored in magnetic fields

what is kinetic energy

the energy a moving object has due to its motion

what does the amount of kinetic energy depend on

the objects mass (heavier objects have more kinetic energy if they’re moving at the same speed) and velocity (Faster objects have way more kinetic energy — because velocity is squared in the formula. velocity affects KE the most)

how does potential energy turn into kinetic energy

1. when an object starts high up, it has max PE and 0 KE (bc its not moving yet)

2. the object begins to fall, gravity pulls it downward so it accelerates, the PE decreases and KE increases, the energy is transferring from GPE → KE

3. just before hitting the ground, the object has max KE bc its moving the fastest, its potential energy is almost 0 (height is almost 0)

so, as height decreases, pe turns into ke and as speed increases ke increases

what are the types of kinetic energy

1. sound

2. heat

3. light 

4. motion

what r the conditions for a chemical reaction to take place

particles collide with energy greater than the activation energy and particles collide at the correct orientation

use collision theory to describe the relationship between temperature and the rate of a chemical reaction

at low temp, a higher fraction of collisions have low energy, so the rate is slower

what is mechanical energy

the energy of an object in motion or the energy that is stored in an object due to its position

define work

the change in mechanical energy of an object, calculated by multiplying force and displacement

what is energy transfer

energy is moved from one place to another without changing form, e.g. placing an ice cube in water transfers thermal energy to the ice cube

what is energy transformation

a change in the form of energy, e,g, rollercoasters work bc of a continuous change between kinetic energy and gravitational potential energy (GPE)

explain energy transformation in a heater

when u turn on an electrical heater, it takes electrical energy from the wall and transforms it into thermal energy to warm up ur room. it also produces some light energy, which is why you can see parts of it glowing

how to draw an energy flowchart

1. list the energy types present in a given situation

2. write the starting energy

3. draw an arrow pointing away from the starting energy

4. write the ending energy (or energies)

Consider a falling soft drink can. It starts with some gravitational potential energy, which is converted into kinetic energy as it falls.

Draw an energy flowchart for this situation

gravitational potential energy → kinetic energy

how to find the efficiency of an energy transformation

useful output energy (J) divided by input energy (J) x 100%

can a system be more than 100% efficient

no

what does a sankey diagram represent

the ratio of efficiency.

• the height of each section represents the proportions of energy forms

• the total amount of energy is equal at every stage of the transformation

when a question asks “type/method of energy transfer” what do y talk about and explain

it asks about how the energy moves, the main ones are

1. conduction(energy transferred through direct contact like spoon to hand)

2. convection (energy transferred by movement of fluids like liquid or air)

3. radiation (energy transferred by electromagnetic waves which means no contact needed eg sun and firelight)

what is the suffix ide reserved for

ionic compounds (metal and non metal conjoined) or simple covalent compounds. only the non-metal element whose always written second ends with ide

what are the suffixes ate and ite reserved for

polyatomic ions, when a polyatomic ion loses an oxygen, their suffix changes from ate to ite

what is nitrate

NO3-

what is sulfate

SO4 2-

what is carbonate

CO3 2-

what is phosphate

PO 4 3-

what is hydroxide

OH-

ammonium

NH4+