What we did in class today: Friday January 6th, 2012

• Took notes over Newton’s 2nd & 3rd Laws• Demonstrations with the laws.• Reminder to study note cards and energy study guides for test

week over Energy, metrics and scientific method on Tuesday.www.studystack.comClick on Physical ScienceGo to Page 9Metrics/scientific methodMrs. Shafter’s Motion VocabularyMrs. Shafter’s Electromagnetic SpectrumMrs. Shafter’s Waves

Unit C pgs. 49-55 (11.2) Force and Mass Determine Acceleration

Review1. What stops the motion of a sled moving down

a snowy hill?

The sled stops moving when acted

upon by an unbalanced force such

as friction.

I. Newton’s second law relates force, mass and acceleration.

2. Why is more force needed to accelerate a shopping cart full of groceries than the same cart when its empty?

Because the mass of the shopping cart full of groceries has more mass than the empty cart, more force is needed to accelerate the full cart than the empty cart with the same acceleration.

A. Newton’s Second Law3. Write two factors that determine the acceleration of an object.

The mass of the object and

the size of the force applied.

4. As you increase the force on an object, the acceleration ______________________.

As you increase the mass of an object, the acceleration ___________________________.

The direction of acceleration is ______________________ the direction of the force.

increases

decreases

the same as

B. Force Equals Mass Times Acceleration5. Force = mass x accelerationWhat force is needed to accelerate a 20 Kg wheelbarrow 4 m/s2 ?Mass of wheelbarrow= 20 Kg

Acceleration of the wheelbarrow = 4 m/s2

Calculate the force. F= 80N

6. Acceleration = Force / mass

Zack pulls a loaded wagon with a force of 4N. If the wagon has a mass of 5 kg, what is its acceleration?

Force = 4 N

mass = 5 kg

Calculate the acceleration = .8 m/s2

C. Mass and Acceleration

7. If you pushed a volleyball and a balloon with the same force, explain which would have the greater acceleration.

The balloon would have the greater acceleration because it has less mass than the volleyball. Objects with less mass accelerate more.

II. Forces can change the direction of motion.

8. Applying a force to an object can result in three things. Complete the main ideaChart with the three results of applying a force to a soccer ball.

Apply a force to a soccer ball.

The soccer ball may speed up

The soccer ball may slow down

The soccer ball may change

direction

A. Centripetal Force9. Draw a picture showing the meaning of centripetal force. Draw an arrow to show the direction of the force.

B. Circular Motion and Newton’s Second Law

10. You grab a string with a ball attached to it and whirl the ball in a circle over your head. In which direction are you pulling the string? If you pull harder on the string, what happens to the acceleration of the ball?

You are pulling the string toward the

Center of the circle.

The acceleration of the ball increases.

Unit C 11.3 Forces Act in PairsHighlight the Key Concept and Vocabulary

Mass and force.

As the bat meets the ball, it exerts a force upon it andpushes the ball forward. The ball exerts an equal butopposite force on the bat that pushes it backward.

The action force is the diver pushing down on the board.

The reaction force is the board pushing up on the diver.

•Action and reaction forces act on different objects.

• Action and reaction forces are equal and opposite.

•Balanced forces act on a single object. •Balanced forces are equaland opposite.

The rope will remain at rest until unbalanced forces act upon it (Newton’s first law). If the forces remain balanced, everyone will stay in the same place and the rope willremain still. The forces are contact forces.

The four-member team will likely win the competition. Due to the extra team member, this side will be able to exert a greater force on the rope than the team with threemembers (Newton’s second law).