physics small def

• Scalar


  A quantity that has magnitude/size
• Vector


  A quantity that has magnitude/size and direction
• Accuracy


  How close a reading is to its true value. When readings are accurate, the peak / average value moves towards the true value
• Precision


  Smallest change in value that can be measured by an instrument. OR Spread of values / measurements (scatter between each data is relatively small/ lines are closer together / sharper peak)
• Random errors


  Readings have positive and negative values around the peak value / values are scattered / wide range. To reduce errors, take several readings to get an average value.
• Systematic Error


  The average / peak is not the true value / the readings are not centred around the true value. Look/check for zero error to avoid systematic error.
• Uncertainty


  The range of value within which a measurement is likely to be in.
• Acceleration (vector)


  Rate of change of velocity.
• Displacement (vector)


  is the straight line distance between start and finish points (in that direction) / minimum distance
• Distance (scalar)


  is the actual path travelled
• Free Fall


  The downward motion of an object under the influence of force of gravity with a constant acceleration (g = 9.81 ms-2).
• Projectile motion


  Objects acted upon by a force with a vector perpendicular to its horizontal velocity. Assume zero frictional forces. Trajectory of the object will result in a parabola.
• Speed (scalar)


  Distance travelled per unit time taken
• Terminal velocity


  Constant speed of object when resultant force is zero due to large air resistance.
• Velocity (vector)


  Rate of change of displacement
• Conservation Of Momentum


  Total momentum of (an isolated) system (of interacting bodies) remains constant, provided there are no resultant external forces (e.g. friction)
• Elastic Collisions


  Total momentum and total Kinetic Energy of a system is conserved. Relative speed of approach is equal to the relative speed of separation
• Force


  It is defined as the rate of change of momentum of a body
• Impulse


  It is the product of a force & the time during which the force is applied.
• Inelastic Collisions


  Total momentum of a system is conserved, but the total Kinetic Energy is not conserved. Speed before impact is not equal to speed
• Linear Momentum


  Product of an object's mass & velocity, with its direction always being the same as the direction of velocity.
• Mass

  It is a measure of inertia of a body or the property of a body that resists change in motion
• Newton's 1st Law


  A body remains at rest or constant velocity unless acted on by a resultant (external) force
• Newton's 2nd Law


  The (resultant) force is proportional to the rate of change of momentum
• Newton's 3rd Law


  If one body exerts a force on another, it will experience a force by the other body, which is equal in magnitude & opposite in direction. Both forces are of the same kind.
• Weight


  Weight is the force due to the gravitational field
• Centre Of Gravity


  The point on an object at which the entire weight of the body seemingly acts. It is the point at which the Earth actually applies the pull of gravity.
• Density


  Amount of mass per unit volume of a substance.
• Equilibrium


  Net / resultant force and moment is zero (OR sum of clockwise moments = sum of anticlockwise moments). If the triangle of forces is 'closed' then there is no resultant force and the object is in equilibrium.
• Moment / Torque

  Product of the force and the perpendicular distance to the pivot
• Pressure


  The perpendicular/normal force applied per unit area
• Principle Of Moments


  The sum of the clockwise moments about a point equals the sum of the anticlockwise moments (about the same point)
• Torque Of A Couple


  Product of one of the forces and perpendicular distance between forces. (The turning effect is caused by two equal & opposite forces when their line of actions are different.)
• Upthrust


  It is the resultant force on a submerged object due to the pressure difference between the higher pressure at the bottom of the object and the lower pressure at the top of the object immersed in a fluid.
• Energy


  It is the stored ability to do work.
• Work Done


  Product of a force & the distance moved in the direction of the force.
• Gravitational Potential Energy


  Energy stored due to height/position of mass
• Internal Energy


  It is the total of the microscopic Kinetic & Potential energies of particles of a material.
• Kinetic Energy


  Energy of an object due to its motion.
• Potential Energy


  Energy stored by an object to do work