Force/Motion NOTES

Force and Motion Notes

AKS :   14c -  Define speed as a rate and define velocity as speed in a given direction

SPEED

  • MOTION only takes place when a force has been applied to matter. A FORCE is a push or pull
  • A REFERENCE POINT is generally a stationary object such as a tree, street sign, building etc.
  • An object is in motion if it changes position over time when compared with a reference point.
  • SPEED depends of distance and time.
  • The rate at which an object moves is called its SPEED.
  • Speed is the distance and object travels in a certain amount of time.
  • The SI unit for speed as meters per second m/s.  Other units used to measure speed include: Kilometers per hour  (km/h), miles per hour (m/h), feet per second (f/s)
  • The formula to calculate speed is :  AVERAGE SPEED = TOTAL DISTANCE

TOTAL TIME

DISTANCE = SPEEDx TIME

TIME= DISTANCE /SPEED

Example: If the distance is 100km and it takes a car 2hrs to

travel the distance, what is the speed of the car?

Speed = Distance                 




  • Constant Speed means the speed of an object is not increasing or decreasing, but remains consistent or the same over time.

AKS 14c1- perform calculations involving speed, time and distance to interpret distance-time graphs as representations of constant velocity or acceleration

  • Distant Time graphs are used show the speed of objects. Time is plotted on the x-axis and distance is plotted on the y-axis. View the examples below.


  • High speedmath expressionLow speed

If an object is not moving, a horizontal line is shown on a distance-time graph. Time is increasing to the right, but its distance does not change. It is not moving. We say it is At Rest.

If an object is moving at a constant speed, it means it has the same increase in distance in a given time: Time is increasing to the right, and distance is increasing constantly with time. The object moves at a constant speed. Constant speed is shown by straight lines on a graph.

Two moving objects: Both lines in the graph show that each object moved the same distance, but the steeper dashed line got there before the other one: A steeper line indicates a larger distance moved in a given time. In other words, higher speed. Both lines are straight, so both speeds are constant.



AKS 14c2 – determine the relationship between velocity and acceleration

VELOCITY

  • The speed of an object in a particular direction is the object’s VELOCITY.
  • Velocity changes when the speed or the direction of an object changes.
  • An objects velocity is constant only if its speed and direction don’t change.
  • Constant velocity is always along a straight line.
  • Velocity is expressed in meters per second m/s.
  • Velocity must include both speed and direction. Example: An airplane’s velocity is 600km/h south.
  • Circle the example of velocity – 25m/s forward, 1500km/h, 55m/h northeast, 70km/h.

ACCELERATION

  • ACCELERATION is the rate at which velocity changes.
  • It is also how fast velocity changes. The faster velocity changes, the greater the acceleration is.
  • Acceleration of an object also changes if its speed or its direction changes.
  • Anything that’s moving in a straight line( no change in direction) at a constant speed( no change in speed is not accelerating.
  • Acceleration is expressed in meters per second per second. (m/s/s)
  • To calculate acceleration we use the following formula:

Acceleration = Final Velocity (V2)  - Initial Velocity (V1)

                                                            Time

  • For example:  If a car obtains a velocity of 60km/hr in 10seconds, what is its acceleration?

Acceleration = Final Velocity (V2)  - Initial Velocity (V1)

                                                        Time

                              =     60km/hr  - 0km/hr      

                                               10sec

                      =   60km/hr                          =   6km/hr/sec

                            10sec          

  • Positive Acceleration measures a change in velocity of a moving object in which velocity increases or it is speeding up.
  • Deceleration is simply negative acceleration. It measures a change in velocity of a moving object that is slowing down. Example when brakes are applied to a car, it is decelerating.
  • Velocity has direction, so velocity changes if your direction changes. Therefore a change in direction is acceleration, even if there is no change in speed.
  • CENTRIPETAL ACCELERATION is acceleration that occurs in a circular motion.
  • Examples of Acceleration:
  • A braking car (changing speed but not direction)
  • A car that’s speeding up( why do you think they call that pedal an accelerator)
  • Your mom’s expensive piece of china that your just dropped(watch it speed up as it falls to the floor)
  • A dog chasing its tail ( change in direction)
  • A roller coaster nearing the end of a vertical loop ( change in direction and quite possibly a change in speed)

Graphs that show acceleration look different from those that show constant speed.  The line on this graph is curving upwards. This shows an

increase in speed, since the line is getting steeper. In other words, in a given time, the distance the object moves is change (getting larger). It is accelerating.

The graph is not a straight line so you can tell you are accelerating. The acceleration is also not constant for each second.





AKS  14 -  investigate the relationship between force, mass and the motion of objects

AKS 14a – determine the relationship between force, mass and the motion of objects

AKS 14b – demonstrate and explain the effect of balanced and unbalanced forces on an object in terms of gravity, inertia and friction (Newton's Laws of Motion as they pertain to everyday

FORCES

  • FORCE is a push or pull. All forces are exerted on one object by another object.
  • Force is expressed in newtons (N)
  • NET FORCE is the force that results from combining all forces exerted on an object.
  • BALANCED FORCE is one in which the net forces equal zero. There is no motion.  For example: During a tug-of war, if the teams are equal in strength, the forces pulling on both ends of the rope are equal and there is no movement. The forces are balanced with a net force of zero.
  • UNBALANCED FORCE has a net force greater than zero. Unbalanced force produces a change in motion. Unbalanced forces cause a non-moving object to start moving.
  • INERTIA – is the tendency of objects to resist a change in motion. Inertia is why we wear seat belts. If a car is travelling at 70km/h and comes to a sudden stop, the people inside the car continue moving at 70km/h unless a force prevents their forward motion through the windshield.
  • The more mass and object has, the more inertia it has and the greater the force it takes to change its motion.
  • Mass affects inertia.  An object with a large mass has more inertia than an object with a small mass. Changing the motion of an object with a large mass is harder than changing the motion of an object with small mass. Pushing a grocery basket loaded with groceries is harder than pushing it empty. Stopping a train moving at 60km/h also takes longer than a car moving at the same speed because the train has more mass.
  • Mass is a measure of an object’s inertia.
  • Small mass = large acceleration
  • Large mass = small acceleration
  • Small force  = small acceleration
  • Large Force = large acceleration
  • FRICTION is a force that opposes the motion of an object. Friction opposes motion when two surfaces are touching. The contact reduces the speed of the moving object and releases heat.
  • Rougher surfaces create more friction.
  • Greater forces create more friction. The amount of friction depends on the force pushing the surfaces together. If force is increased, friction between the surfaces also increases.

TYPES OF FRICTION

  • Sliding Friction - Sliding friction is when two solid surfaces slide against each other. Putting a book flat on a desk and moving it around is an example of sliding friction.
  • Rolling Friction - A force which opposes the motion of any object which is rolling over the surface of another. Example anything on wheels – roller skates, cars, trains, planes
  • Fluid Friction - Fluid friction is the friction between a solid object as it moves through a liquid or a gas. Example swimming, a fast moving car through the air.
  • Static Friction - Friction between two objects in contact that are not moving.

REDUCING FRICTION

  • Use Lubricants – motor oil, grease, oil, wax, (gas lubricant comes out of the tiny holes on an air hockey table)
  • Switch from sliding to rolling friction. ( ball bearing are places inside the wheels of inline skates and bicycles to make it easier for the wheels to turn)

INCREASING FRICTION

  • Make the surface rougher. ( We added sand  to the icy streets  to keeps the cars from skidding)
  • Increase the force pushing the surfaces together. (Place a heavy rock on the newspaper on the park bench so that it will not be blown away.)
  • is the amount of mater in an object and its value does not change. It is constant.