Chapter2Section3

=__**Chapter 2 Section 3**__= toc __**Newton's Second Law: Push or Pull**__

__**Learning Outcomes**__

 * identify: the forces acting on an object
 * determine: when the forces on an object are either balanced or unbalanced
 * compare: amounts of acceleration semi-quantitatively
 * apply: Newton's second law of motion
 * apply: the definition of the newton as a unit of force
 * describe: weight as the force due to gravity on an object

__**What Do You See?**__

 * she is pushing the ball and as it begins to roll you have to speed up to catch the ball
 * the dog begins walking then running then driving

__**What Do You Think?**__
What is a force? How will the same amount of force affect a tennis ball and a bowling ball differently?
 * a push or pull on an object
 * the tennis ball will go faster and further while the bowling ball will go slower and not as far
 * the ball with the larger mass will be less effected by the force

__**Investigate**__
2. small bend a. The cart goes in a straight line at a slow constant speed.

3. large bend a. The cart is going in a straight line at a constant speed. (it is a little faster now) b. The motion is similar between the two, they both go at a constant speed and in a straight line. c. The larger the bend the faster the cart goes. d. The greater the constant force pushing on an object, the faster the object will go.

4. a. We used a pencil with a mass smaller than the cart. When the pencil is pushed by the ruler it accelerates faster because it has a smaller mass.

5. a. metal pole- It is harder to start moving, but once it is moving it will take a larger force to stop it. water bottle- Is harder to start moving, but does not continue to keep moving because it does not have wheels and is not round. (it will not roll and can not move on its own) b. When equal amounts of a constant force are used to push objects having different masses, the more massive object will not more as far or as fast.

6. a.
 * push on a large object with a small force :a large object can push a small force
 * push on a small object with a large force: a small object can not push a large force

8. a. Then penny stay on the ruler, but the ruler bends down. b. Every time you add a penny to the ruler the bend gets larger and by the second penny is added it falls off. One penny is a small force and three pennies is a large force. c. The ruler bends down because of gravity.

__**Physics Talk**__
a=F/m F: force expressed in newtons (N) m: mass expressed in kilograms (kg) a=F/m F=ma m=F/a (does not matter what kind of force it is or how it originates) Newton's Second Law of Motion relates to... -another type of force is gravity F(gravity)=ma(gravity) w=mg
 * Newton's Second Law of Motion:** the acceleration of an object is directly proportional to the unbalanced force acting on it and inversely proportional to the object's mass. The direction of the same as the direction of the unbalanced force.
 * acceleration= force/mass**
 * Unbalanced forces:** newton's second law says that it is caused by this
 * Calculations** (using newton's second law of motion)
 * force, mass, and acceleration
 * a=F/m
 * F=ma
 * m=F/a
 * weight**: the vertical, downward force exerted on a mass as a result of gravity
 * Calculations**
 * m: the mass in kilograms
 * g: the acceleration due to gravity (9.8 m/s^2)
 * free-body diagram**: a diagram showing the forces acting on an object
 * Balanced and Unbalanced Forces**
 * when one force acts on another it accelerates
 * when 2 forces act at the same time the direction and magnitude of the forces determine the motion of the object
 * all of the forces are in the same direction then the sum of the forces or net force will cause a greater acceleration (than either force alone)
 * there can be a net force of zero acceleration when two forces are in opposite directions

__**Checking Up**__
The acceleration of an object is directly proportional to the unbalanced force acting on it and inversely proportional to the object's mass. The direction of the acceleration is the same as the direction of the unbalanced force. If you want to keep a constant force and the object's mass increases then you have to decrease the acceleration. Because gravity is -9.8 m/s^2. Your weight would increase, but your mass would stay the same.
 * 1. Describe Newton's second law of motion in your own words.**
 * 2. For a constant force, what effect does increasing an object's mass have on its acceleration?**
 * 3. An object weighs 30N. How would you explain this statement according to what you know about mass and acceleration due to gravity?**
 * 4. If you went to a planet with a higher acceleration due to gravity, what would happen to your weight? What would happen to your mass?**

__**Physics To Go: (1-7,10-12, 15)**__
2. a. The table above does not follow where acceleration matches g which is the acceleration due to gravity (-9.8m/s^2). b. It should be negative when using acceleration due to gravity. c. Yes because it is an unbalanced force that is acting on the running back. 3. What is the acceleration of a 0.30kg volleyball when a player uses a force of 42N to spike the ball? F=ma 42N=(.30kg)a a=140m/s^2 4. What force would be needed to accelerate a 0.040kg golf ball at 20m/s^2? F=ma F=(0.040kg)(20m/s^2) F=0.8 N 5. a. Newton's First Law: an object in motion at a constant speed and travel in a straight line unless another force acts on it b. Newton's Second Law: (Force=mass*acceleration) the acceleration of an object is directly related to the force acting on the object and inversely proportional to the object's mass (a bowling ball has a larger mass and weight so once it begins to move it is harder to stop then a baseball) 6. mass: 0.1kg w=mg w=(.1)(-9.8) w=-.98N Newton 7. weight in newtons=(weight in pounds)(4.38 newtons per pound) a. ?=150*4.38 657N b. w=mg (to calculate in kg) 657=m(-9.8) m= -67.04 kg 10. -10N 11. 800N 12. F=ma 700g=0.7kg 125N=(.7kg)a a=178.57 m/s^2 15. w=mg w=(12.8kg)(-9.8m/s^2) w= -125.44N
 * newton's second law || F || m || a ||
 * sprinter beginning 100-m dash || 350N || 70kg || 5m/s^2 ||
 * long jumper in flight || 800N || 80kg || 10m/s^2 ||
 * shot-put ball in flight || 70N || 7kg || 10m/s^2 ||
 * ski jumper going downhill before jumping || 400N || 80kg || 5m/s^2 ||
 * hockey player "shaving ice" while stopping || -1500N || 100kg || -15m/s^2 ||
 * running back being tackled || -3000N || 100kg || -30m/s^2 ||

__**#13,14,16,17**__ __**(all work in my notebook)**__

__**Review Notes 1/3/12**__
__**(all notes in my notebook)**__

__**Do Now: 1/4/12**__
What is the acceleration of a 0.4kg volleyball, when a player spikes it with a force of 65N? F=ma 65N=(0.4kg)a a= 162.5m/s^2

__**Physics Plus**__
(#1,2) __**(all work in my notebook)**__