Science in motion

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Science in motion

• NEWTONS LAWS OF MOTION

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Forces and Newtons

• A force is a push or a pull that can cause
  acceleration to happen in an object
• We measure forces with the unit know as a NEWTON
  (which is the force needed to cause a 1 kilogram
  object ti accelerate at 1m/s2)

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Frame of Reference

• A frame of reference is the perspective from
  which a system is observed.
• Whenever you describe something as moving you are
  comparing it to a frame of reference that is
  assumed to be stationary.
• There are NO truly STATIONARY objects in the
  universe

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Combining Forces
- The Nature of Force

• The combination of all forces acting on an object
  is called the net force.

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Unbalanced Forces
- The Nature of Force

• Unbalanced forces acting on an object result in a
  net force and cause a change in the objects
  motion.

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Balanced Forces
- The Nature of Force

• Balanced forces acting on an object do not change
  the objects motion.

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1st law Law of Inertia

• Things keep on moving the way they are moving"
  (unless acted upon by an unbalanced force).

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Newtons First Law of Motion

• Law of Inertia A body remains at rest or moving
  in a straight line unless acted upon by some
  unbalanced force

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• Imagine a place in the cosmos far from all
  gravitational and frictional influences. Suppose
  that an astronaut in that place throws a rock.
• a The rock will
• gradually stop.
• b. continue in motion in the same direction at
  constant speed.

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Mr. Wegley

• Mr. Wegley spends most Sunday afternoons at rest
  on the sofa, watching pro football games and
  consuming large quantities of food. What effect
  (if any) does this practice have upon his
  inertia? Explain.

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Moose attack

• Ben Tooclose is being chased through the woods by
  a bull moose which he was attempting to
  photograph. The enormous mass of the bull moose
  is extremely intimidating. Yet, if Ben makes a
  zigzag pattern through the woods, he will be able
  to use the large mass of the moose to his own
  advantage. Explain this in terms of inertia and
  Newton's first law of motion.

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Newtons 2nd Law of Motion

• F ma A force F applied to a body with mass m
  will cause it to accelerate (change speed and/or
  direction) at rate a.
• Or the harder the push or pull the greater the
  acceleration

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F MA

• Force Mass x Acceleration
• Force is measured in units called Newtons (N)
• A Newton (N) is to the force needed to make a
  1Kilogram object accelerate at 1
  meter/second/second
• NKg m/s2

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Inertial mass Gravitational mass

• In elephant-feather scenario, we can say that the
  elephant experiences a much greater force (which
  tends to produce large accelerations. Yet, the
  mass of an object resists acceleration.
• Thus, the greater mass of the elephant (which
  tends to produce small accelerations) offsets the
  influence of the greater force
• It is the force/mass ratio which determines the
  acceleration

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Newtons 3rd Law

• Action and Reaction Every force (or action)
  applied, creates a second equal but opposite
  force (or action) back on the first body.

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Newton's Third Law of Motion

• This law is demonstrated by what happens if we
  step off a boat onto the bank of a lake as we
  move in the direction of the shore, the boat
  tends to move in the opposite direction (leaving
  us facedown in the water, if we aren't careful!).

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Gravity
- Friction and Gravity

• Two factors affect the gravitational attraction
  between objects mass and distance.

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Gravity
- Friction and Gravity

• The force of gravity on a person or object at the
  surface of a planet is known as weight.

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Free Fall
- Friction and Gravity

• Use the graph to answer the following questions.

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Free Fall
- Friction and Gravity

• Interpreting Graphs
• What variable is on the horizontal axis? The
  vertical axis?

• Time is on the horizontal axis, and speed is on
  the vertical axis.

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Free Fall
- Friction and Gravity

• Calculating
• Calculate the slope of the graph. What does the
  slope tell you about the objects motion?

• The slope is 9.8. The speed increases by 9.8 m/s
  each second.

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Free Fall
- Friction and Gravity

• Predicting
• What will the speed of the object be at 6 seconds?

• 58.8 m/s

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Free Fall
- Friction and Gravity

• Drawing Conclusions
• Suppose another object of the same size but with
  a greater mass was dropped instead. How would the
  speed values change?

• The speed values would not change.

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Air Resistance
- Friction and Gravity

• Falling objects with a greater surface area
  experience more air resistance.

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Gravity From Newton to Einstein
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G6.67x10-11N
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R2GM/speed of light squared
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• If I have seen further than other men, it is by
  standing on the shoulders of giants.
• Isaac Newton, Letter to Robert Hooke, February 5,
  1675

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Newtons Words

• I do not know what I may appear to the world but
  to myself I seem to have been only like a boy
  playing on the seashore, and diverting myself,
  now and then in finding a smoother pebble or a
  prettier shell than ordinary, whilst the great
  ocean of truth lay all undiscovered before me.
• Sir Issac Newton(1643-1727)

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Speed distance and Time

• (1) SpeedDistance/time
• (2) Distance Speed x time
• (3) Time distance/speed
• (4) Accel (Vf Vi)/time

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Force mass and acceleration equations

• If ForceMass x acceleration
• (5) Fma
• Then
• (6) F/macceleration
• And
• (7)F/amass