Force and Motion

• scalar quantities


  quantities that describe distance/magnitude but do not include direction
• vector quantities


  have both magnitude and direction
• resultant force formula


  mass x acceleration
• terminal velocity


  - the maximum velocity attainable by an object as it falls through a gas/fluid.

  
  

  - It occurs when the sum of the air resistance is equal to the downward force of gravity acting on the object.

  
  

  - Since the net force on the object is zero, the object has zero acceleration.
• Type of force: reaction force


  the force between any two objects in contact (like the upwards force from a table on a book)
• Hooke's Law


  The law stating that the stress of a solid is directly proportional to the strain applied to it.
• Type of force: gravitational/weight


  the force between any two objects with mass (like the Earth and the Moon)
• Type of force: electrostatic


  the force between any two objects with charge (like a proton and an electron)
• Type of force: Upthrust


  the upward force on any object in a fluid
• Type of force: air resistance


  the force of friction between objects falling through the air
• Type of force: tension


  forces that stretch an object
• Type of force: compression


  forces that squeeze an object
• How can forces affect an object ?


  - speed (forces can cause bodies to speed up or slow down)

  
  

  - direction (forces can cause bodies to change their direction of travel)

  
  

  - shape (forces can cause bodies to stretch, compress, or deform)
• thrust


  push suddenly or violently in a specified direction ( the force pushing a vehicle)
• Examples of scalar quantities


  - Speed

  - Distance

  - Mass

  - Temperature

  - Time
• example of vector quantities


  - displacement

  - velocity

  - acceleration

  - forcemass x gravity
• Weight equation


  mass x gravity
• Force equation


  mass x acceleration
• Friction


  A force that opposes motion between two surfaces that are in contact
• Stopping distance


  Thinking distance + braking distance
• factors affecting a vehicle's stopping distance


  - Vehicle speed

  
  

  - Vehicle mass

  
  

  - Road conditions ( wet or icy roads make it harder to decelerate)

  
  

  - Driver reaction time

  (Being tired, or intoxicated (i.e. alcohol, or drugs) can increase reaction time)
• Hooke's Law Equation


  Force = spring constant x extension
• elastic deformation


  When objects return to their original shape when the stretching force is removed

  (eg. Rubber bands, Fabrics, Steel springs)
• Inelastic deformation


  When objects remain stretched and do not return completely to their original shape even when the stretching force is removed

  (eg. Plastic, Clay, Glass)
• Acceleration equation


  change in velocity/time
• Average speed equation


  total distance/total time
• uniform acceleration equation


  final velocity^2 - initial velocity^2 = 2 x acceleration x distance
• practical investigate motion of everyday objects method


  1. measure out a meter

  2. drop paper cone and measure time it takes to reach the ground

  3. repeat then repeat with different heights
• practical investigate motion of everyday objects results


  use average speed equation to find the speed at which the paper cones fell
• Investigating springs and rubber bands equipment

  - clamp stand

  - ruler

  - spring

  - 5 x 100g weights

  - 100g hanger

  - pointer
• Investigating springs and rubber bands method


  - Set up the apparatus as shown in the diagram, initially without any masses hanging from the spring / rubber band

  
  

  - Align the marker to a value on the ruler, record this initial length of the spring / rubber band

  
  

  - Add the 100 g mass hanger onto the spring / rubber band

  
  

  - Record the mass (in kg) and position (in cm) from the ruler now that the spring / rubber band has extended

  
  

  - Add another 100 g to the mass hanger

  
  

  - Record the new mass and position from the ruler now that the spring / rubber band has extended further

  
  

  - Repeat this process until all masses have been added

  
  

  - Remove the masses and repeat the entire process again, until it has been carried out a total of three times, and an average length (for each mass attached) is calculated
• Investigating Metal Wires equipment

  - metal wire

  - ruler

  - 5 x 100g weights

  - 100g hanger

  - tape marker

  - bench pulley

  - G clamp and wooden blocks
• Investigating Metal Wires method


  - Set up the apparatus so the wire is taut. No masses should be attached just yet

  
  

  - Measure the original length of the wire using a metre ruler and mark a reference point with tape preferably near the beginning of the scale eg. at 1 cm

  
  

  - Record the initial reading on the ruler of the reference point

  Add a 100 g mass onto the mass hanger

  
  

  - Read and record the new reading of the tape marker from the meter ruler now that the metal wire has extended

  
  

  - Repeat this process until all masses have been added

  
  

  - Remove the masses and repeat the entire process again, until it has been carried out a total of three times, and an average length (for each mass attached) is calculated
• Investigating Metal Wires and Investigating springs and rubber bands results


  minus the length of the extended wire/ spring with at each weight and minus from it the original length of the wire.

  
  

  - then plot the amount they extended for each length on a line graph

  
  

  - Draw a line or curve of best fit

  
  

  - If the graph has a linear region (is a straight line), then the force is proportional to the extension