# Motion and Forces Chapter 2.

## Presentation on theme: "Motion and Forces Chapter 2."— Presentation transcript:

Motion and Forces Chapter 2

Bell Work 1/21/10 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.

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

Bell Work 1/25/10 Please begin completing the Map Practice Packet. Write your answers for each question on your yellow bell work sheet for today. PLEASE DO NOT WRITE IN THE PACKET

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.

Describing Forces forces are describe according to: strength and
direction

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!

Balanced Force equal forces acting in opposite directions
* balanced forces will NOT change the object’s motion!

Newton’s First Law An object at rest will remain at rest unless acted upon by an unbalanced force!

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

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.

Law of Inertia Newton’s first law is often referred to as the Law of Inertia. Inertia is a property that describes an object’s 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 kg.

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 object’s inertia.

Bell Work 1/26/10 Please answer #1-4 on page 47 in the book.

Force 2.2 Notes Newton’s Second Law of Motion
Explains a relationship between force, mass and acceleration Often expressed as: force = mass x acceleration Simply stated: An object’s acceleration depends on the mass of an object and the strength and direction of the force acting on it.

Force = mass x acceleration
Units: acceleration – m/s/s mass – kg force – kg x m/s/s or Newton (N)

Rearranging the Force Equation
To calculate mass: Mass = ___force___ acceleration To calculate acceleration: Acceleration = force mass

Using the formula acceleration = force/mass
We know the following: as force increases, acceleration increases. as mass increases, acceleration decreases. to get an object to accelerate, you must increase force or decrease mass.

Bell Work 1/27/10 – choose the correct word to fill in the blanks: force, inertia, motion, net force, Newton’s first law, unbalanced force _______ is the change of position over time. The overall force acting on an object when all forces are combined is called _____ A force that can change the motion of an object is called a(n) ________. A(n) _______ is a push or a pull. 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 ____. The resistance of an object to a change in speed or direction is called_______.

Bell Work 1/28/10 Fill in the blanks
If you increase the force on a box, it will have _______ inertia. You push two chairs in a straight line with the same force. One chair is more massive than the other. The more massive chair will have _______ acceleration. Any force that is keeping an object moving in a circle is known as ______. Acceleration is ________.

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

Newton’s Third Law – states that for every action there is a reaction
Force Notes 2.3 Newton’s Third Law – states that for every action there is a reaction

Bell Work 2/2/10 – Please get a new green bell work sheet!
Identify the action/reaction force pair involved when you catch a ball. Explain the difference between balanced forces and action/reaction forces. 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?

Bell Work 2/4/10 – Look back in your notes for the formulas or in the book pg 51-53
A model rocket is accelerating a 6 m/s2. The force on it is 2 N. What is the mass of the rocket? 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? A girl pushes a 10 kg shopping cart with a force of 30 N. What is the acceleration of the cart?

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

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 ball’s momentum? Example 3 – What is the momentum of a 0.5 kg ball moving at 0.5 m/s?

• Momentum is a property of a moving object.

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?

• Forces in collisions are equal and opposite.

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.

• Momentum is conserved in collisions.
total momentum

Bell Work – 2/5/10 Complete # on page 71. You only have to write the letter of the answer.