Forces and Motion: Scalars, Vectors, and Gravity

• Forces causes a change in an object's speed/direction, but are not needed to keep a moving object in motion.

Scalar and vectors

• Scalars have magnitude
• Vectors have both magnitude and direction
• Displacement is distance with a specific direction
• Vectors are shown with an arrow indicating direction and magnitude

Contact and Non-Contact forces

• Forces are a push or pull due to interaction with another object.
• Contact forces involve objects that physically touch, like friction, tension, air resistance, and normal contact force.
• Non-contact forces involve objects that are separated such as gravitational, electrostatic, and magnetic forces.

Gravity and Weight

• Gravity is the force of attraction on all objects.
• Weight is the force acting on an object due to gravity, dependent on the gravitational field strength at the object's location.
• Objects on Earth's surface experience a gravitational force of 9.8N per kilogram of mass.
• Weight can be calculated using a newton meter or by the formula: weight = mass x gfs
• The weight of an object is considered to act at a single point, called the center of mass.

Resultant Forces

• A resultant force is a single force with the same effect as all original forces acting together.
• Balanced forces occur when the resultant force is 0N, resulting in constant speed or a stationary object.

Free Body Diagrams

• Objects are shown as points
• Forces are shown as arrows starting at different points

Vector Diagrams

Steps to draw a vector diagram:

• Pick a scale
• Use a protractor to measure angles
• Draw vectors connecting to the end of the previous vector
• Connect vectors to make a parallelogram and draw a line from the tails of the parallelogram vectors to the opposite end.
• Measure the length and convert using the scale

Resolving Force

• A single force can be resolved into two components acting at right angles
• The two component forces have the same effect as the single force
• Use the scale to measure the magnitude of the resolving force by measuring the length of the force.

Work Done and Energy Transfer

• Energy is transferred when a force is applied; for example, chemical energy from a person is transferred to thermal energy in a box when pushing it.
• Work done against frictional forces increases the thermal energy of the object.
• Work is done when a force causes an object to move.
• Work done is calculated as force multiplied by distance along the line of action of the force.
• 1 Nm is equal to 1 Joule (1J) of work done.
• When a driver applies brakes, kinetic energy is transferred to the thermal energy store of the brakes due to friction.

Forces and Elasticity

• When stretching or compressing an elastic object, work is done, and elastic potential energy is stored in the object.
• Work done = elastic potential energy only when the object is not inelastically deformed.
• Force is calculated as the spring constant multiplied by the extension.
• Extension is directly proportional to the force applied up to the limit of proportionality.
• A linear relationship indicates a straight line, while a curved line indicates a nonlinear relationship between force and extension.

Elastic Deformation

• Elastic deformation occurs when an object returns to its original length and shape once the forces are removed.
• Pulling on both ends of an elastic material stretches it, while pushing compresses it.
• Applying three forces, with one in the opposite direction, will cause the object to bend.
• To change an object's length or size, multiple forces must be acting on it.

Inelastic Deformation

• Inelastic deformation occurs when an object does not return to its original length after forces are removed (e.g., polymers).
• If a spring is overstretched, it exceeds the limit of proportionality and undergoes inelastic deformation.
• Extension remains directly proportional to force as long as the limit of proportionality (Hooke's Law) is not exceeded.

Moments

• A moment is a turning effect of a force
• Examples include wheelbarrows, crowbars, seesaws, and cranes.
• Moment (Nm) is calculated as force multiplied by the perpendicular distance to the pivot.
• The distance must be perpendicular from the line of action of the force to the pivot.

Balanced Moments

• Clockwise moment about a pivot equals the anticlockwise moment about that point.
• An unbalanced moment results in the object toppling.

Levers and Gears

• Levers are force multipliers where a larger force is applied to the load over the supplied force.
• Gears transfer turning force, e.g., from an engine to wheels.
• If gear B has twice the radius of gear A it will have twice the turning effect but gear A rotates twice as much.
• Turning forces depend on the distance between the edges of the gears to the center.

Pressure in Fluids

• Fluids include gases and liquids.
• Pressure of a fluid is the force exerted normal to a surface divided by the area of that surface.

Atmospheric Pressure

• Atmosphere refers to the layer of air around the earth.
• Atmospheric density declines with increasing altitude.
• Atmospheric pressure results from air molecules colliding with surfaces.
• Pressure reduces with increasing height due to fewer air molecules.

Pressure in a Column of Liquid

• Water at the bottom of a container has higher pressure because depth increases and there is a greater weight of water acting downwards.
• Pressure in a liquid column is determined by height x density x gravitational field strength.
• Pressure increases with an increase in the density of the liquid.
• Greater density liquids correspond to a greater weight of water pushing down.

Floating or Sinking

• When submerged, the bottom of an object experiences greater pressure compared to the top, resulting in an upward force called upthrust.
• For an object to float, upthrust must equal the object's weight.
• If upthrust is less than the object's weight, the object will sink.
• Lowering an object into water displaces water, causing water levels to rise.
• Upthrust is equal to the weight of the water displaced.
• If an object displaces its own weight of water, the upthrust will equal the object's weight, causing it to float.

Speed

• Distance (scalar) only indicates how far an object moves.
• Displacement (vector) indicates the distance and direction traveled in a straight line.
• Speed (scalar) is calculated as distance divided by time.
• Typical speeds: walking is 1.5m/s, running is 3m/s, and cycling is 6m/s
• Factors that affect this consist of age, terrain, fitness, and distance travelled.
• Sound travels around 330m/s, but this may vary in the air.
• Sound travels faster on warmer days than on cooler days.

Velocity

• Velocity is speed in a specific direction and is a vector quantity.
• Use the same equation for speed to calculate velocity.

Motion in a Circle

• An object moving at a constant speed in a circle has changing direction, and thus, constantly changing velocity.

Distance-Time Graph

• Represents the distance travelled by an object moving in a straight line.
• The gradient indicates speed
• A curve shows acceleration or deceleration.
• Speed can be determined by drawing a tangent at a particular time and calculating the gradient.

Acceleration

• Acceleration is the change in velocity over time
• Acceleration (m/s²) is calculated as the change in velocity (m/s) divided by time (s)
• Gradient indicates acceleration
• Straight line indicates constant velocity
• Upward sloping line indicates constant acceleration
• Downward sloping line indicates constant deceleration
• Negative numbers indicate deceleration
• Total area indicates distance
• If accelerating at a constant rate: final velocity^2 - initial velocity^2 = 2 x acceleration x distance.

How Objects Accelerate Towards the Earth

• Objects accelerating towards Earth initially accelerate at 9.8 m/s² due to gravity
• As an object falls, it experiences air resistance from air particles
• Over time, air resistance balances out with gravity, resulting in terminal velocity.
• Terminal velocity depends on the object and the shape can alter the terminal velocity
  • Greater friction from shape = lower terminal velocity

Newton's First Law

• An object will remain stationary, or continue moving with the same velocity, unless acted upon by a resultant force
• If there is driving force on the left then their has to be a equal force to the right, the net force has to be zero if they are at a constant seed
• Resistive forces include friction with air and the road
• A resultant force changes an object's speed or direction.
• Inertia is the natural tendency of an object to resist changes in its motion.

Newton's Second Law

• States that the acceleration of an object is proportional to the resultant force acting on the object, and inversely proportional to the object's mass.
• Greater force = greater acceleration
• Larger mass = smaller acceleration
• Expressed by the equation: force = mass x acceleration
• Cars typically travel at 13 m/s on main roads and 30 m/s on motorways.

Intertial Mass

• Is the measure of how difficult it is to change the velocity of an object
• Defined as the ratio of force needed to move an object over the force produced
• Large inertial mass requires a larger force to achieve a given acceleration

Newton's Third Law

• Whenever two objects interact, the forces exerted on each other are equal and opposite.
• Example: A wheel driving exerts a force in the reverse direction on the road and the road exerts an equal force forwards on the wheel.

Forces on a Skydiver

• Initially, the only force acting on a skydiver is weight, which remains constant.
• Weight causes the skydiver to have a resultant force downwards causing acceleration
• The skydiver experiences friction with air particles (air resistance) in the upwards direction which is lower than weight.
• As velocity increases, air resistance increases until it balances out with the skydiver's weight.
• When air resistance balances with the skydiver's weight the skydiver reaches terminal velocity
• Upon opening the parachute, surface area increases and air resistance increases
• Air resistance becomes greater than weight, causing a resultant force upwards (deceleration)
• As velocity decreases, air resistance also decreases until it balances with weight
• The skydiver falls at a lower terminal velocity which is safe

Stopping Distance

• Stopping distance is the total distance traveled between when an obstruction is first seen and when the vehicle stops.
• Stopping distance = thinking distance + braking distance
  • Thinking distance: distance traveled while the driver reacts.
  • Tiredness, distractions (e.g., phone), alcohol, and drugs increase reaction time, thus increasing thinking distance.
  • Braking distance: distance traveled while brakes are applied.
  • Wet, icy conditions, worn tires, and worn brakes reduce friction, thus increasing braking distance
• The greater the speed = the greater the stopping distance
• Typical reaction time ranges from 0.2 to 0.9 seconds.
• Reaction time can be measured with a ruler drop test.

Breaking

• Pressing the brakes transfers kinetic energy to the thermal energy store of the breaks causing the brakes to increase in temp and the car slowing down due to loss in kinetic energy
• Greater speed requires greater braking force to stop the vehicle within a given distance
  • Large speeds = large braking force which causes car to decelerate causing large amounts of kinetic energy to be transferred to thermal and possible driver loss of control

Momentum

• All moving objects have momentum. An object not moving has zero momentum.
• Momentum is calculated as mass x velocity.

Conservation of Momentum

• In a closed system, the total momentum before an event equals the total momentum after the event.
• A rapid change in momentum can be extremely dangerous.
• Car crash are designed to test safety features (e.g., belts, airbags, and crumple zones).
• During a crash rapid momentum changing can lead to death
• Can reduce danger in crashes by increasing the collision time.

Safety Features

• Safety features include airbags, seatbelts, crash mats, helmets, and cushioned surfaces, and aim to slow the change in momentum.

Waves

• Waves transfer energy
• Transverse waves (e.g., ripples in water) have vibrations perpendicular to energy transfer.
• Longitudinal waves (e.g., sound in air) have vibrations parallel to energy transfer.

Properties of Waves

• Amplitude: maximum displacement of a point on a wave from its undisturbed position.
• Wavelength: the distance from a point on one wave to the equivalent point on the adjacent wave.
• Frequency: the number of waves passing a point per second.
• Period = 1 / frequency
• Wave speed is the speed at which energy is transferred, or the wave moves through the medium.
• Wave speed = frequency x wavelength

Measuring Speed of Waves

• Sound in air:
  • Create a noise and measure the time for the echo, then use s = d/t.
  • Two microphones connected to data logger at a large distance record time difference
• Ripples on water surface:
  • Use a stroboscope, measure the fixed ripple space, and use the wave speed formula.
  • Move a pencil along paper and at the same speed to measure the drawn line time

Relationships between Waves

• Increasing frequency increases velocity
• Increasing wavelength increases velocity
• Period is inversely proportional to frequency.
• Smaller period equals higher frequency and greater velocity.

Reflection of Waves

• Waves reflect off flat surfaces, strongest when the surface is smooth.
• Angle of incidence equals the angle of reflection.
• Light reflects if an object is opaque and not absorbed by the material.
• Electrons absorb and remit light energy as reflected waves

Transmission

• Waves pass through transparent materials.
• Highly transparent materials allow more light to pass through.
• Refraction causes waves to pass through a material but the process may stop waves emerging.

Absorption

• If the frequency of light matches the energy levels of electrons, light will be absorbed.
• Light is absorbed by electrons and re-emitted as heat over time.
• If a material appears green, only green light from the spectrum has been reflected to our eyes.

Sound Waves

• Sound is caused by vibration in solids.
• In the ear cause the eardrum an other parts to vibrate which causes a sound
• Works over limited frequencies (20Hz - 20,000Hz).
• When waves move mediums there speeds can change
• Travel faster in solids as particle are much closer
• If speed changes the wavelength changes

Viewing Sound

• View features by connecting a microphone to a cathode ray oscilloscope.
• CRO shows sound waves as transverse but sound waves are longitudinal.
• High frequency means high pitch.
• Low frequency means low pitch.
• Small amplitude means quiet.
• Large amplitude means loud.
• Only moves between mediums has wound moves vibrating particles
• Reflected sounds are echo's

Ultrasound

• Sound wave with frequencies higher than humans
• At least 20000Hz
• Partially happens at boundary of 2 densities
• Time take for reflection to reach the detector
• Creates images of organs eg heart and kidneys
• Can't if sorounded by bone
• No mutations no cancer risk
• Can be used to determine distance

Seismic Waves

• Produced by earth quakes

• Follow curved paths because of density changes

• Patterns gives us information on interiors

• P Waves

  • Longitudinal
  • Pass solid through liquid
  • Go faster waves.

• S waves

  • Travel only through solid
  • Travel through the uper creast

• P waves tell s that outer layers can be either solid

• S tell us that some layers are solid

Electromagnetic Waves

• Do not need a medium
• Transverse waves
• Travel at a the same speed 300,00,000m/s

Energy Transference

• Transfer energy to be absorbed
• Eg use microwaves to transfer energy to absorb heat

Electromagnetic spectrum

• Low frequency → High frequency: radio → Microwaves → Infrared → Visible → Ultraviolet → X - rays→ gamma rays.
• Visible light is only apart of the electromagnetic spectrum that can be detected by the human eye.
• Different part of the spectrum either absorbed/transmit or reflect
• Eg food contain water molecules which absorbs micrometers when they are metal they reflect
• Different objects absorb the spectrum differently eg
• Eg light waves aborbed by black reflects by shiny
• What happends to the waves depend on wavelength

Refraction Of Electromanetic Waves

• Can change direction by there speeds
• This is called refraction
• When traveling speeds need to be reduced.
• Speeding up travels tend to bend.
• This makes it appear bent
• Angle cannot change unless right angle to the surface

Properties of Electromanetic Waves

• When em waves are generates changes happens in atoms
• Can either increase or decrease amount
• A change to an atom generate em wave

Hazards

• Ultar violet can case the increased ageing
• Increased risk of cancer
• damage depends on type and dose (measures in sieverts

Em wave uses

• Radio waves can be used with terrestrial devises -Microwaves can travel in between hills. -Microwaves used to heat food
• Infrared is used ti determine if their are building leaks
• Visible light is used with optical fibres
• Uv short wave lengh great energy
• x-rays can be used to determine broken
• gamma rays can be used to identify broken caners