Science exam semester one year 10

Balanced forces

• Forces that are equal in size and opposite in direction

• They cancel each other out

• No change in motion or shape

• Object may be still or moving at a constant speed

• Example: A book resting on a table (gravity pulls down, table pushes up)

Unbalanced Forces

• Forces that are not equal

• Cause a change in motion (speed up, slow down, change direction)

• Example: Two dogs pull a toy — if one dog pulls harder, the toy moves

Representing the forces on an object

• Forces are shown with arrows

• Arrow length = size of force

• Arrow direction = direction of force

• If the object is not moving or not accelerating, forces are balanced

Applied Force

• A push or pull by a person, animal, or machine

• Example: Holding a soccer ball — your hand applies a force upward

• Balances gravity, so the ball doesn’t fall

Free Body Diagram

• Object is shown as a square or box

• Arrows show forces acting on it

• Helps find the net force

Balanced Forces in Free Body Diagram

• Equal length arrows in opposite directions

• Forces cancel → net force = 0

• No movement or constant speed

Support Force

• The upward force from a surface

• Balances gravity when something rests on a surface

• If object doesn’t sink → support force

Net force

The sum of the forces acting on a single object

• If the forces are balanced, the net force is zero → no change in motion.

• If the forces are unbalanced, the net force is not zero → the object will accelerate (speed up, slow down, or change direction).

• add any forces acting in the same direction and subtract any forces acting in opposite directions.

• units of net force are newtons (N).

• 10 N force right, 6 N force left → Net force = 4 N to the right

• 5 N up, 5 N down → Net force = 0 N (balanced)

Newton’s first law of motion

Law of inertia- An object will remain at rest or move with constant velocity unless acted on by a net force

Properties of inertia

• Inertia is not a force

• It doesn't make something move or stop

• It's a property of all objects with mass,

Moving vs stationary objects and inertia

• Inertia is the natural tendency of an object to keep doing what it's already doing

• An object at rest → stays at rest

• A moving object → keeps moving at the same speed and direction

• Inertia means an object resists changes to its motion

Velocity

Velocity = speed + direction

• A change in velocity means a change in speed, direction, or both

• Inertia keeps an object’s velocity the same unless a net force acts on it

Newton’s Second Law of Motion

• Newton’s 2nd Law: F = ma
  (Force = mass × acceleration)

Proportional Relationships (F=ma)

• When the force acting on an object increases, the acceleration also increases.
  → This means acceleration is directly proportional to force.
  (More force = more acceleration)

Force Units

• 1 Newton (N) = 1 kg × 1 m/s² (f=ma)

• Standard units:

  • Force (F) → Newtons (N)

  • Mass (m) → Kilograms (kg)

  • Acceleration (a) → Metres per second² (m/s²)

• Simulation uses:

  • millinewtons (mN) = 0.001 N

  • grams (g) = 0.001 kg

• F = ma still works if you divide both mass and force by 1000

Why More Mass Needs More Force

• More mass = more inertia

• Inertia = resistance to change in motion

• A greater force is needed to accelerate a larger mass

• So: same force → smaller object accelerates more

Newton’s Third Law

• Every action has an equal and opposite reaction.

• Forces always come in pairs.

• These pairs are called action-reaction forces.

Action-Reaction forces must be:

• equal in size

• opposite in direction

• of the same type

• acting on different objects

• e.g. a horse pulls a cart (action), the cart pulls back on the horse (reaction). They don’t cancel out because they act on different things.

Labelling forces

Each label should have the following form:

F_{force type, x on y}

For example, you hit a nail with a hammer. We could represent the force like this:

F_{applied, hammer on nail}

Action reaction forces vs balanced forces

• Equal and opposite forces only cancel out when they act on the same object.

• This is when we say that they are balanced.

• But, the pairs of forces described by the third law always act on different objects.

What is speed?

• Speed describes how far something travels in a certain amount of time.

Speed Formula

speed= distance travelled/time taken

Converting between units of speed

To convert km/h → m/s, divide by 3.6

To convert m/s → km/h, multiply by 3.6

Units of speed- option 1

Speed- m/s

Distance- m

Time- s

Units of speed- option 2

Speed- km/h

Distance- km

Time- h

Instantaneous speed

An objects speed at any instant of it’s motion.

Average speed

The average of the instantaneous speeds over the whole distance travelled.

Average speed=Distance/Time

Transposing speed equation

What does a distance–time graph show?

How far an object has travelled over time.

x axis= time

y axis= distance

gradient= speed

How to read a distance-time graph

• Upward curve (steepening) = Speeding up

• Curve flattening out = Slowing down

• Straight line = Constant speed

• Flat horizontal line = Stopped

How does the slope of a distance–time graph relate to speed?

The steeper the slope, the greater the speed.
The slope = speed.

How do we calculate average speed between two times?

• Speed=gradient

• s= rise(distance)/run(time)

• speed= d₂​−d_1/ t₂-t₁

• Change in distance/ change in time

What does a speed–time graph show?

How fast an object is moving at each moment.

How to read a speed-time graph

• Upward slope (line going up)
  → Acceleration (speed is increasing)

• Downward slope (line going down)
  → Deceleration (speed is decreasing)

• Horizontal line (flat)
  → Constant speed

• Line at zero (on the time axis)
  → Object is stopped / not moving

Distance

Total distance travelled during the motion

Displacement

Straight line distance from an object’s starting point

• has magnitude(size) and direction.

• e.g. it's 120 km by a slow and winding road between Snake Gully and Gusville. But the map shows Gusville is only 70 km east of Snake Gully.

• So, the displacement from snake gully to Gusville is 70km east

Scaler quantity

Has magnitude(size) but not direction

• Distance is a scalar quantity

• Speed is a scalar quantity, because it is measured using distance and time, which are both scalar quantities.

Vector quantity

Has magnitude(size) and direction

• Displacement is a vector quantity.

• Velocity is a vector quantity

Velocity formula

Velocity= displacement/time

e.g. A map shows Gusville is only 70 km east of Snake Gully.

If it takes a driver 2 hours to get between the towns, then their average velocity is: 70/ 2

= 35km east

What's the difference between average speed and average velocity?

Speed = uses distance
Velocity = uses displacement
They’re often different!

Positive and negative velocity

Choose a direction as positive.

• Move that way = positive velocity

• Move opposite = negative velocity

( Right and up is often positive, left and down is often negative)

What is Acceleration?

Acceleration = any change in velocity
Velocity = speed + direction

It is a vector quantity
So, acceleration happens when:

• 🚀 Speed increases

• 🐢 Speed decreases

• 🔄 Direction changes

Acceleration Formula

Acceleration= change in velocity/time taken

a= v₂-v₁/t₂-t₁

Standard units of acceleration

a= m/s/s, m/s² , or ms^-2

v= m/s or ms^-1

t=s

Positive vs Negative Acceleration

• Positive acceleration = speeding up

• Negative acceleration = slowing down (also called deceleration)
  ⚠ But if you're moving in a negative direction, negative acceleration can mean speeding up in that direction!

Velocity-Time graphs: slope

The slope (tilt) tells you the acceleration:

• Upward slope = Positive acceleration (speeding up in + direction)

• Downward slope = Negative acceleration (slowing down or speeding up in – direction)

• Flat line = Constant velocity- same speed and direction (zero acceleration)

Velocity-Time graphs- other important info

On a velocity-time graph:

• Area under the line = distance travelled

• Slope of the line = acceleration

  • Steeper = faster acceleration or deceleration

  • Flat = no acceleration

What is acceleration due to gravity?

• The same force that acts on all objects on Earth.

• Acceleration due to gravity (g) has a value of about 10 m/s/s down.

• It always acts downwards towards the centre of the Earth, no matter the direction the object is going

Why would an object have a negative acceleration even when going up?

Because gravity pulls it down the whole time,

• Slows it down going up

• Speeds it up coming down

What does a straight, sloping line mean on a velocity-time graph?

• Constant acceleration

• Negative slope = acceleration is downward

• Line goes through 0 when an object changes direction

Physical change

A change in matter that does not form new substances.

Examples of physical changes

Change in

• Position

• Shape

• Size

• State

Chemical change/reaction

A change in matter that forms one or more new substances.

Examples of chemical changes

• release of light or sound

• Formation of a new gas

• Change in colour

• Disappearance of a solid

• Formation of a new solid

• Change in temperature

Atom

The smallest particle of an element

Molecule

A group of atoms bonded together

Fixed formula, e.g. O2, H2O

Chemical bond

An attractive force that holds two atoms together

Mixture

A combination of substances that can be physically seperated.

Element

a pure substance made up of only one type of atom.

Compound

Made up of two or more different types of atoms bonded together, such as carbon dioxide (CO₂) and sodium chloride (NaCl).

Chemical equation

Reactants—>Products

e.g. sodium + oxygen → sodium oxide

Reactants

The substances that react with each other

Products

The new substances formed by a reaction

The re-arrangement of atoms

• During a chemical reaction, some of the chemical bonds between atoms are broken and new bonds are formed.

• This re-arrangement of atoms is what produces a new substance.

• The same elements are present after a reaction – they're just arranged in a new way.

Metal atom

1, 2, or 3 electrons in outer shell

Non-metal atom

5, 6 or 7 electrons in outer shell

Lattice

Continuous arrangements of bonded atoms in regular patterns.

• Ratio of elements, e.g. NaCl, Au

Why do elements bond together?

Atoms form chemical bonds to obtain full valence shells.

• By bonding together in chemical reactions, atoms can reach a more stable state.

Ions

Charged particles, which are formed when atoms either lose or gain electrons

Cations

Positively charged ions formed by the loss of electrons

Anions

Negatively charged ions formed by the gain of electrons

Ionic bonds

• The transfer of electrons from one atom to another results in two ions with opposite charges. The attraction between these opposite charges is what makes an ionic bond.

• Occurs between metals and non metals

• Metal cations

• Non-metal anions

Predicting ionic compounds

E.g: Aluminium + Chloride

Aluminium- Metal, charge of 3+

Chloride- Non-metal, charge of 1-

This means you need three negative charges to balance out the positive charge of three.

(Al³⁺)+ (Cl⁻)+ (Cl⁻)+ (Cl⁻)

= AlCl₃

• metals are always written before non-metals

Metallic bonding

• When metals bond with metals, they donate their valence electrons into a common pool.

• This results in metal cations floating on a sea of delocalised electrons

• The positively charged metal ions (cations) are held together by the attraction to this sea of delocalized electrons.

Properties of metals explained by metallic bonding- Electrical Conductivity

Delocalised electrons can move freely through the metal- a flow of electrons is an electric current

Properties of metals explained by metallic bonding- Heat Conductivity

The delocalised electrons carry thermal energy (heat) through the metal quickly and easily.

Properties of metals explained by metallic bonding- Shine

Delocalised electrons move quickly so that light can reflect off all surfaces of the metal.

Covalent bonding

When non-metals bond with non-metals, they share a pair of electrons between atoms.

• Each atom contributes one or more electrons to form a shared pair.

• One pair represents two total electrons

• This sharing allows both atoms to achieve a stable electron configuration (a full outer shell).

How to represent covalent bonding

F-F, H-H, H-O-H

• The number of lines between the element symbols represent the number of bonds

Bonds of common elements

H, F, Cl- single bond ( two electrons are shared)

O- double bond(four electrons are shared)

N- triple bond( six electrons are shared)

C- quadruple bond( 8 electrons are shared)

Law of Conservation of Matter

• In a chemical reaction, atoms are not created or destroyed.

• Total number of atoms of each element remains the same before and after the reaction.

• The bonds of the atoms are just rearranged in different ways, forming new substances.

Unbalanced Equations

• An equation is unbalanced if the number of atoms of each element is not the same on both sides.

Example (Unbalanced Thermite Reaction):
Fe₂O₃ + Al → Fe + Al₂O₃

• The number of Fe and Al atoms do not match.

Balancing equations

An equation is balanced when the number of each type of atom is the same on both sides.

To balance an equation:

• Adjust the numbers in front of chemical formulas (coefficients).

Example (Balanced Thermite Reaction):
Fe₂O₃ + 2Al → 2Fe + Al₂O₃

Subscripts and coefficients in chemical equations

• When balancing an equation, you can’t change the subscript numbers, as this shows how the molecule is naturally formed.

• You can only adjust the coefficients, which change the number of elements or compounds in a chemical equation.

• To find the amount of each type of atom, multiply the coefficient by the subscript

How to balance equations

Composition reactions

• Two or more reactants combine to form a single product.

• General form: A + B → AB

• Examples: N₂+3H₂→2NH₃, 2Mg+O₂→2MgO

multiple reactants, single product

Decomposition reactions

• One reactant breaking down into multiple products

• General form: AB→ A + B

• Examples: 2H₂O→2H₂+O₂, CaCo₃→ CaO+CO₂

Single reactant, multiple products

Displacement reaction

• One element replaces another in a compound

• General form: AB+C→BC+A

• Examples Zn+CuSO₄→ZnSO₄+Cu, Cu + AgSO₄→2Ag+CuSO₄

One metal dissolving, another coming out of solution

Often two metals involved

Neutralisation reaction

• Acids and bases reacting together

• General form: Acid + base→water + salt

• Examples: HCl+ NaOH→H₂O+NaCl, H₂SO₄+Mg(OH)₂→2H₂O + MgSO₄

Acid, base

Precipitation reactions

• Two solutions are mixed and a solid forms

• General form: AB+CD→ AD+CB (one product is solid)

• Examples: Pb(NO₃)+2KI→ PbI₂+2KNO₃

Solid forms from mixing solutions

Three main types of chemical bonding

• metal + metal → metallic bonding

• metal + non-metal → ionic bonding

• non-metal + non-metal → covalent bonding

Collision theory

• The idea that the re-arrangement of atoms requires collisions between the reactant particles.

• It's only when the particles are in contact that new bonds can form to make the products.

What a successful collision involves

Particles colliding with both

• the right orientation, and

• enough energy, or speed, to break their bonds

If both conditions aren't met then the particles will just bounce off each other without reacting.

Rate of a reaction

• How quickly reactants are converted into products.

• The higher the frequency of successful collisions, the higher the reaction rate.

What you need to increase the rate of a chemical reaction:

• surface area

• temperature

• concentration

These all increase the chance of a successful collision

Surface area

• Surface area is the total outside area of a three dimensional solid.

• As a solid is broken into smaller prices, the surface area increases.

• When the surface area is increased, the chance of reactant particles colliding increases, so there are more reactions and the reaction is faster.

Temperature

• When the temperature is increased, the average kinetic (movement) energy of the particles is increased, so particles move faster.

• More collisions occur, and more particles have enough energy to react. This means there are more reactions and the reaction is faster.

Concentration

• Concentration is how many particles there are per unit volume.

• When the concentration is increased, the chance of reactant particles colliding increases, so there are more reactions and the reaction is faster.