forces

• Force - push or a pull. It changes the:

  -Shape

  -speed

  -direction

  
  

  of an object
• Contact forces - forces that need to touch the object to make the force affect it.

  EXAMPLES: air resistance, water resistance, upthrust.
• Non-contact forces: forces that affect objects from a distance.

  EXAMPLES:

  Gravity: pulls objects downwards.

  Static electricity: attracts objects

  Magnetism: attracts objects made out of iron and other metals and repel metals.
• The measure for force is Newtons (N) and arrows can be used to show the direction of the force. A bigger arrow = greater force.
• Weight - force of gravity pulling on you. This is measured in Newtons as it is a force.
• Mass is the amount of matter that makes up an object. It is measured in kilograms and grams.
• The force of gravity on earth is greater than in the moon. The earth's gravity pulls on every kilogram with a force of 10 N.
• Materials can be stretched or compressed. The amount of stretch of compression in a material depends on:

  -type of material

  -amount of force
• Springs are made out of coils of wire. the extension of a spring is the difference between its original length and the extended length.
• Elasticity = when an object returns to its original shape when force is removed.
• The idea that extension is proportional to the force is known as Hooke's Law. The extension and force is proportional to a certain point, known as the limit of proportionality.
• Elastic limit - when enough force is applied to a spring and will no longer return to its original shape.
• Objects who do not change back to their original shape after a force is removed are plastic objects.
• Springs are used inside spring meters.
• Friction: force between 2 touching objects. It can slow things down or make things stay still.
• Adding a lubricant allows friction to be reduced - known as lubrication.
• Friction can wear things away. Friction due to gases and liquids can also cause them to slow down.
• Pressure is the amount of force pushing on a certain area.
• Pressure depends on:

  -size of the force

  -size of the area it is pushing on

  If the size of the force is the same:

  -Larger area, lower pressure

  -Smaller area, higher pressure

  If you keep the area the same:

  -Smaller force, lower pressure

  -Larger force, higher pressure.
• Calculating pressure: Force/area

  This is measured in Newtons and area is measured in square meters. The unit is N/m2. This is also known as Pascal (Pa)
• Cm2 can also be used in measuring pressure if the size is small.
• Forces can add together. If 2 forces are the same size, then nothing will change and the forces are balanced. If the force is stronger than the other, something will start to move, this is unbalanced forces.
• If unbalanced forces act on a moving object, the speed will change.
• Stationary objects have balanced forces on them. Moving objects also have balanced forces, but if the speed changes, then there is unbalanced forces.
• Turning effect of a force is known as moment.
• Turning forces acts at a certain distance from the pivot - a fixed point
• Moment depends on:

  -force applied and perpendicular distance from the pivot.

  Force (Newtons) x perpendicular distance (meters)= moment
• Moment has a clockwise and anticlockwise movement. #
• Law of moments: when a object is in equilibrium, the sum of the clockwise moment = anti-clockwise moment.
• Hooke's Law!:

  Force = spring constant (N/m) x extension (m)
• Hooke's law is valid for all elastic materials but the spring constant is different for each object.