Motion and Forces

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Motion and Forces

• Chapter 2

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Bell Work 1/26/11

• Copy each of these statements onto your bell work
  sheet. Then decide if they are true or false.
  If false correct them.
• Speed includes direction, while velocity does
  not.
• A moving object covers the same distance in less
  time if its velocity is greater.
• Acceleration measures only change in speed.

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Bell Work 1/22/10

• Please begin working on your foldable or
  PowerPoint
• On your bell work sheet write down working on
  project for today

4
Bell Work 1/27/11

• Please answer 1-13 in the MAP practice packet by
  the sinks. Write your answers for each question
  on your bell work sheet for today. PLEASE DO NOT
  WRITE IN THE PACKET

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Force 2.1 Notes

• forces occur when one object pushes or pulls on
  another object
• We say that one object exerts a force on another
  object to cause it to accelerate.

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Describing Forces

• forces are describe according to
• strength and
• direction

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Two types of Forces

• Unbalanced Force
• two forces acting in the same direction
• OR
• One stronger force acting in the opposite
  direction of a weaker force.
• Unbalanced forces cause an object to accelerate!

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• Balanced Force
• equal forces acting in opposite directions
• balanced forces will NOT change the objects
  motion!

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Newtons First Law

• An object at rest will remain at rest unless
  acted upon by an unbalanced force!

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continued

• An object moving at constant velocity will
  continue moving at constant velocity unless acted
  upon by an unbalanced force.

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Inertia Lab Questions

• Before you start this experiment, see if you can
  decide which egg is the raw one and which egg is
  the hard boiled one. Place the eggs on the two
  plates and start them spinning at the same time.
  The egg that continues spinning for the longest
  time is the hard boiled egg.
• Steps for the 1st experiment
• 1. Place the uncooked egg on a plate and start it
  spinning. 2. Touch it lightly with your
  fingertip to stop the egg spinning.3. Once the
  egg stops take your finger away immediately.
• What happens to the egg? The shell of the egg
  actually stops spinning but the inside (yolk and
  egg white) keeps spinning. Because the inside of
  the raw egg is a liquid, it makes the egg start
  to spin again. This force is called inertia.
• Steps for the 2nd experiment
• 1. Place the hard-boiled egg on a plate and start
  it spinning.2. Touch it lightly with your
  fingertip to stop the egg spinning.3. Once the
  egg stops take your finger away immediately.
• What happens to the egg? The boiled egg stops
  spinning because the inside contents of the egg
  are a solid mass.
• Steps for the 3rd experiment
• 1. Place both eggs on the plates (one on each
  plate). 2. Start both eggs spinning at the same
  time.3. Place your finger on each egg at the
  same time to quickly stop them spinning.4. Let
  go of both eggs at the same time.
• Now you can compare how the hard-boiled egg stops
  spinning and the raw egg keeps spinning.

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Law of Inertia

• Newtons first law is often referred to as the
  Law of Inertia.
• Inertia is a property that describes an objects
  resistance to changes in motion.
• if an object is moving, inertia keeps it moving.
• if an object is at rest, inertia keeps it at
  rest.

• Mass is the amount of matter in an object.
• Mass is a measure of inertia.
• the more mass an object has the more inertia it
  has. This means it will take more force to get
  it to accelerate.
• the opposite is also true less mass, less
  inertia, less force.
• mass is measured in grams.

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How are mass and inertia related?

• The more matter in an object, the harder it is to
  get the object to accelerate or you could say the
  harder it is to overcome the objects inertia.

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Bell Work 1/28/11

• Please answer 1, 2, and 4 on page 47 in the book.

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Bell Work 1/31/11 choose the correct word to
fill in the blanks force, inertia, motion, net
force, Newtons first law, unbalanced force

1. _______ is the change of position over time.
2. The overall force acting on an object when all
   forces are combined is called _____
3. A force that can change the motion of an object
   is called a(n) ________.
4. A(n) _______ is a push or a pull.
5. Objects at rest remain at rest, and objects in
   motion remain in motion at the same velocity,
   unless acted on by an unbalanced force. This
   statement describes ____.
6. The resistance of an object to a change in speed
   or direction is called_______.

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Force 2.2 Notes

• Newtons Second Law of Motion
• Explains a relationship between force, mass and
  acceleration
• Often expressed as force mass x
  acceleration
• Simply stated An objects acceleration depends
  on the mass of an object and the strength and
  direction of the force acting on it.
  
  

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Force mass x acceleration

• Units
• acceleration m/s/s
• mass kg
• force kg x m/s/s or Newton (N)

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Practice

1. If a 5 kg ball is accelerating 1.2 m/s2, what is
   the force on it?
2. A person on a scooter is accelerating 2m/s2. If
   the person has a mass of 50 kg, how much force is
   acting on that person?

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• 3. If a team pulls with a combined force of 9000N
  on an airplane with a mass of 30,000kg what is
  the acceleration of the airplane?
• 4. Half the people on the team decide not to pull
  the airplane. The combined force of those left
  is 4500 N, while the airplanes mass is still
  30,000 kg. What is the acceleration?

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• 5. A model rocket is accelerating at 2 m/s2. The
  force on it is 1 N. What is the mass of the
  rocket?
• 6. A boy pushes a shopping cart with a force of
  10 N, and the cart accelerates 1 m/s2. What is
  the mass of the cart?

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• Centripetal force any force that keeps an
  object moving in a circle

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Bell Work 2/7/11 Please use the back of the bell
work sheet from last week

1. What is Newtons First Law of motion?
2. What is Newtons Second Law of motion?
3. Give an example of centripetal force.

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Bell Work 2/8/11

1. A model rocket is accelerating at 6 m/s2. The
   force on it is 2 N. What is the mass of the
   rocket?
2. Another model rocket that has a mass of 15 kg is
   accelerating at 5 m/s2. What is the force being
   applied to the rocket?
3. A girl pushes a 10 kg shopping cart with a force
   of 30 N. What is the acceleration of the cart?

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Force Notes 2.3

• Newtons Third Law states that for every action
  there is a reaction

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Bell Work 2/9/11

1. Identify the action/reaction force pair involved
   when you catch a ball.
2. Explain the difference between balanced forces
   and action/reaction forces.
3. A man pushes on a wall with a force of 50 N. What
   are the size and the direction of the force that
   the wall exerts on the man?

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Force 2.4 Notes

• Objects in motion have momentum. Which would have
  more momentum a bowling ball being thrown at a
  wall or a tennis ball?
• Momentum A measure of mass in motion. The
  momentum of an object is the product of its mass
  and velocity
• Formula to calculate momentum
• Momentum mass x velocity
• p mv

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Momentum Calculations

• Example 1 - What is the momentum of a 1.5 kg ball
  moving at 2 m/s?
• Example 2 A 6 kg ball is moving with a velocity
  of 2 m/s. What is the balls momentum?
• Example 3 What is the momentum of a 0.5 kg ball
  moving at 0.5 m/s?

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Momentum is a property of a moving object.
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Momentum can be transferred from one object to
another

• If two objects involved in a collision have very
  different masses, the one with the less mass has
  a greater change in velocity.
• Collision a situation in which two objects in
  close contact exchange energy and momentum
• What happens with 2 bumper cars?

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Forces in collisions are equal and opposite.
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Momentum is conserved

• Conservation of momentum states that the total
  momentum of a system of objects does not change,
  as long as no outside forces are acting on that
  system.

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Momentum is conserved in collisions.
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Bell Work 2/10/11

• Complete 11-16 on page 71. You only have to
  write the letter of the answer.

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Bell Work 2/16/11

• Give an example of each of Newtons 3 Laws. Make
  sure to explain in detail how each example
  relates to Newtons Laws.

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Bell Work 2/17/11

• Write complete sentences!
• What is the difference between the momentum of
  bowling ball and a baseball that are moving at
  the same velocities?
• What is the difference between a balanced force
  and an unbalanced force?
• Please get out your study guide and review for
  the test.