P5

• Newtons first law

  If the resultant force on a stationary object is zero, the object will remain stationary. If the resultant force on a moving object is zero, it'll just carry on moving at the same velocity
• Newton's second law

  the acceleration of an object is proportional to the resultant force acting on the object, and inversely proportional to the mass of the object
• Newtons third law

  whenever two objects interact, the forces they exert on each other are equal and opposite
• Vector Quantities

  • force
  • velocity
  • displacement
  • acceleration
  • momentum
• Scalar Quantities

  • speed
  • distance
  • mass
  • temperature
  • time
• A force is a push or a pull on an object that is caused by it interacting with something
• Contact Forces

  • friction
  • air resistance
  • tension
• Non-contact Forces

  • magnetic force
  • gravitational force
  • electrostatic force
• Weight is the force acting on an object due to gravity

  Measured in newtons
• The resultant force is the overall force on a point or object
• when a force moves an object through a distance energy is transferred and work is done on the object
• Elastic objects can stretch, compress or bend

  An object has been elastically deformed if it can go back to it's original shape and length after the force has been removed
• The limit of proportionality is where the extension is no longer proportional to force
• A force or several forces can cause an object to rotate

  The turning effect of a force is called it's moment
• Levers increase the distance from the pivot at which the force is applied. This means less force is needed to get the same moment, making it easier to do work
• Gears

  • teeth interlock so that turning one causes another to turn in the opposite direction
  • used to transmit the rotational effect of a force from one place to another
  • a force transmitted to a larger gear will cause a bigger moment, as the distance to the pivot is greater
  • the larger gear will turn slower than the smaller gear
• As the depth of the liquid increases, the number of particles above that point increases. The weight of these particles adds to the pressure felt at that point, so liquid pressure increases with depth
• When an object is submerged in a fluid, the pressure of the fluid exerts a force on it from every direction
• Pressure increases with depth so the force exerted on the bottom of the object is larger than the force acting on the top of the object. This causes a resultant force upwards, known as upthrust

  The upthrust is equal to the weight of fluid that has been displaced by the object
• If the upthrust on an object is equal to the object's weight, then the forces balance and the object floats
• If an object's weight is more than the upthrust, the object sinks
• An object that's less dense than the fluid it is placed in weighs less than the equivalent volume of fluid

  This means it displaces a volume of fluid that's equal to it's weight before it's completely submerged.

  At this point, the object's weight is equal to the upthrust, so the object floats
• An object that's denser than the fluid it's placed in is unable to displace enough fluid to equal it's weight.

  This means that it's weight is always larger than the upthrust, so it sinks
• Atmospheric Pressure is created on a surface by air molecules colliding with the surface

  As the altitude increases, the atmospheric pressure decreases because the atmosphere gets less dense, so there are fewer air molecules that are able to collide with the surface
• Velocity is speed in a given direction
• Typical Speeds

  • person walking - 1.5 m/s
  • person running - 3 m/s
  • person cycling - 6 m/s
  • car - 25 m/s
  • train - 30 m/s
  • plane - 250 m/s
  • sound - 330 m/s
• Factors Affecting Something's Speed

  • fitness
  • age
  • terrain
• Acceleration is the change in velocity in a certain amount of time
• Uniform acceleration is constant acceleration
• If an object has no force propelling it along it will always slow down and stop because of friction
• friction always acts in the opposite direction to movement
• to travel at a steady speed, the driving force needs to balance the frictional forces
• Drag is the resistance you get in a fluid
• to reduce drag, you can keep the shape of an object streamlined. This is where the object is designed to allow the fluid to flow easily across it, reducing drag
• • when a falling object first sets off, the force of gravity is much more than the frictional force slowing it down, so it accelerates
  • as the speed increases, the friction builds up
  • this gradually reduces the acceleration until eventually the frictional force is equal to the accelerating force
  • It will have reached terminal velocity and will fall at a steady speed
• • air resistance causes things to fall at different speeds
  • terminal velocity of any object is determined by it's drag in comparison to its weight
  • the frictional force depends on it's shape and area
• Inertia is the tendency to continue in the same state of motion
• an object's inertial mass measures how difficult it is to change the velocity of an object
• In a closed system, the total momentum before an event is the same as after the event. This is called conservation of momentum
• when a non-zero resultant force acts on a moving object it causes it's velocity to change. This means that there's a change in momentum

  The force causing the change is equal to the rate of change of momentum

  A larger force means a faster change in momentum