Our Dynamic Universe

• Scalar quantities are quantities that only have a magnitude and do not have a direction. Examples of scalar quantities are:

  • Speed
  • Distance
  • Time
  • Mass
• Vectors are quantities with both direction and magnitude, because of this values with differing direction cannot simply be added and so a resultant vector needs to be calculated via Pythagoras, trig or another method. Examples of vectors include:

  • Force
  • Velocity
  • Displacement
  • Acceleration
• $v=$$s/t$Is this equation used the calculate average velocity or average speed?


  Average velocity
• Does this graph show the object is accelerating or moving at a constant velocity?

  Constant velocity

  
• What does the area under this graph represent?

  Displacement

  
• What does the gradient of this graph represent?

  Acceleration

  
• Is the object accelerating or moving at a constant velocity?

  Accelerating

  
• Displacement graphs form a curve when an object is accelerating or decelerating. When a displacement graph reaches a plateau (straight flat line) the object is stationary, it is lifted off of the x-axis as it is stationary at a certain distance away from the starting point.

  A) Accelerating

  B) Deccelerating

  
• There are four equations of motion which use an objects final and initial velocity, acceleration, displacement and time of travel. They are most often used in projectile motion but they can only be used when the object is travelling with a constant acceleration.
• For freefalling objects (objects that have no additional force acting on them other than gravity and air resistance), the acceleration used in the motion equations is -9.8ms^-1 which is the acceleration due to gravity. The acceleration is negative as the object is falling towards the earth (downwards).
• Below is a displacement-time graph of a ball thrown upwards. Section A shows the ball decelerating as it is thrown upwards while Section B shows the ball accelerating backdown to its starting point. The velocity at the turning point is 0ms^-1 and the displacement is at its maximum.

  
• A projectile is any unpowered object that is thrown or propelled into the air and is effected by gravity. To analyse a projectile's motion we separate its vertical and horizontal components. For the vertical components we use SUVAT equations as we take into account the acceleration due to gravity. Whereas, the horizontal component has a constant velocity so we can use a simple s=ut equation.
• $h =$$v × cos ⁡ θ$ To calculate the horizontal component of velocity, you need to know the magnitude of the velocity and the angle between the velocity vector and the x axis. Think "look across for a tea cosy" to remember if its cos or sin.
• $vert.=$$v×sinθ$ To calculate the vertical component of velocity, you need the magnitude of the velocity and the angle between the velocity vector and the x-axis. Think "look up for a sign" to remember if it is cos or sin.
• There are three types of projectile motion in higher physics: symmetrical, asymmetrical and horizontal launch from a raised platform. Each requires a different approach when calculating the different factors.
• Newtons First Law: An object will remain at rest or continue to move at a constant speed unless acted upon by a resultant force.
• Newton's Second Law: The acceleration of an object is directly proportional to the resultant force acting on it. $F=$$ma$
• Newton's Third Law: For every action, there is an equal and opposite reaction.
• The Conservation of Momentum Law states that the total momentum of an object before and after a collision or interaction is equal, in the absence of external forces. Therefore, in the absence of external forces, the kinetic energy before and after will also be equal.
• There are two types of collision: elastic and inelastic. In elastic collisions, energy is conserved so it is equal before and after the interaction. Whereas, inelastic collisions do not conserve energy and therefore the energy before and after isn't equal.
• When calculating the tension between connected masses, we have to take into account the unit as a whole and then break it into smaller parts. This connects to Newton's 2nd Law as it uses F=ma.
• When calculating the force of an object parallel or perpendicular to the slope we take into account the weight of the object at the angle of the slope from the x-axis. For the parallel component we use: F=mgsinθ; but for perpendicular we use F=mgcosθ.

  A) cos

  B) sin

  C) W=mg

  
• Inertia is the tendency of an object to remain at rest or continue moving in a straight line at a constant speed. All objects have inertia, even if they are not moving.
• When analysing the impact of forces, we usually look at the concept of impulse. Impulse has the equation $Ft=$$mv-mu$ (and is the same as change in momentum), this gives us the average force applied by the object. The SI unit for impulse is Newton seconds (Ns) but kgms^-1 can also be used.
• In higher physics, impulse graphs are almost always triangles- however when friction is take into account the graph is more curved. The area under the graph is the impulse, and the turning point is the maximum force exerted by the object.

  
• The Doppler effect is what causes the pitch of sounds to change as the source moves towards or away from the listener. When an object is traveling towards you it sounds higher pitched, whereas, travelling away from you it sounds lower pitched.

  
• Redshift is a form of the Doppler effect which effects the colour of light. Redshift is evidence for the expanding universe as the light from galaxies becomes more red over time. This is due to the expanding distance between them and therefore expanding wavelength of light. $v=$$λf$
• Blueshift occurs when the light source is travelling towards the observer. Andromeda (our closest galaxy) is an example of a blueshifted light source.
• Hubble's Law connects the relationship between the speed of a galaxy's recession and its distance from Earth. Over time Hubble's constant has changed due to the discovery of more galaxies.
• The faster a galaxy's recessional velocity, the greater it's distance from Earth.
• A closed universe is a universe with a greater mass (and therefore greater magnitude of force holding it together) than the dark energy around it. This means the expansion will decrease and the universe is deemed "closed".
• An open universe is a universe with a magnitude of gravitational force less than that of dark energy (because it doesn't have a great enough mass). This means that the expansion will continue indefinitely and the universe is deemed "open".
• Is our universe considered open or closed?

  Open
• Dark energy makes up 70% of our universe. It is the reason our universe is expanding at an accelerated rate, and is what acts against the force of gravity that tries to pull all matter back to one point.
• In Stellar Temperature graphs, the stars that are the highest temperature have the shortest peak wavelength and emit the most energy across the whole spectrum.

  
• Evidence of the Big Bang:

  • Abundance of light elements
  • Cosmic microwave background radiation
  • Redshift
  • Large-scale homogeneity
• The abundance of light elements was created during the first few minutes of the big bang when temperatures were extremely high. The conditions allowed for nuclear fusion reactions between protons and neutrons which produced helium nuclei. These then combined to form heavier elements such as carbon and oxygen.
• The conditions and extreme temperatures shortly after the Big Bang allowed for nuclear fusion reactions between protons and neutrons which produced light elements. As the universe kept expanding and cooling, these elements spread out and therefore did not undergo further fusion so they are still present across the universe today.
• What were the light elements produced shortly after the Big Bang?

  • Helium
  • Deuterium
  • Lithium
  • Beryllium
• What is the radiation that is present across the universe?

  Cosmic microwave background radiation (CMBR)