Chapter 12

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 Can cause a resting object to move.  It can accelerate a moving object by changing the object’s speed or direction.  SI unit = N (for newton)

 One N is the force that can cause a 1-kg mass to accelerate at a rate of 1 m/s 2  N = 1kg x m/s 2

 Has a net force of 0  No change in object’s motion.  IE: Two Sumo wrestlers of equal weight. Locked head to head and neither one is moving.

 Net force acting on an object is not equal to 0  Object is put into motion and accelerates.  IE: Two sumo wrestlers not equal in weight.

 3 types  Static  Sliding  Rolling tion These 2 symbols mean just listen and look no need to take notes as it will not be tested or it will be shown in the lecture at a later time.

 Force that acts on an objects that are NOT moving.  Acts in the direction opposite to that of the applied force.  IE: You pushing on a world’s largest watermelon that weight 2 tons.

 Force that opposes the direction of motion of an object as it slides over a surface.  IE: You pushing on a really big box of watermelons.

 Force that acts on rolling objects.  Object is bent slightly out of shape.  IE: You pushing a shopping cart full of watermelons….or a little kid you want to terrorize.

 Force that acts between any 2 masses.  Attractive force that pulls objects together.  Can act over large distances.

newton 2. 1 newton newtons newtons

newton 2. 1 newton newtons newtons

1. The answer depends upon the mass of the two groups of people. 2. The answer depends upon the mass of the rope. 3. The answer depends upon the length of the rope. 4. zero

1. The answer depends upon the mass of the two groups of people. 2. The answer depends upon the mass of the rope. 3. The answer depends upon the length of the rope. 4. zero

1. the sum of the forces 2. the product of the forces 3. zero 4. 1 newton

1. the sum of the forces 2. the product of the forces 3. zero 4. 1 newton

1. The net force is positive. 2. The net force is negative. 3. The net force is decreasing. 4. The net force is zero.

1. The net force is positive. 2. The net force is negative. 3. The net force is decreasing. 4. The net force is zero.

Figure Is Net Force 0?Effect on Motion Plant Scale Rope Plant 2

Figure Is Net Force 0?Effect on Motion Plant Yesnone Scale Rope Plant 2

Figure Is Net Force 0?Effect on Motion Plant Yesnone Scale Yesnone Rope Plant 2

Figure Is Net Force 0?Effect on Motion Plant Yesnone Scale Yesnone Rope Yesnone Plant 2

Figure Is Net Force 0?Effect on Motion Plant Yesnone Scale Yesnone Rope Yesnone Plant 2 NoPotted plant accelerates

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 The state of motion of an object does not change as long as the net force acting on the object is zero

 inertia the tendency of an object to resist a change in its motion. In other words, an object at rest tends to remain at rest, and an object in motion tends to remain in motion with the same direction and speed. View 1:52 clip

 The acceleration of an object is equal to the net force acting on it divided by the object's mass Video clip Video clip to “get it” run time 1:45

 An automobile with a mass of 1000 kilograms accelerates when the traffic light turns green. If the net force on the car is 4000 newtons, what is the car's acceleration? What information are you given? M= 1000kg F= 4000N (in the forward direction) A = ?

What information are you given? M= 1000kg F= 4000N (in the forward direction) a = Net force then, 4000N = 4N = 4m/s 2 Mass 1000kg kg

Weight (W) is substituted for force (F) Acceleration due to gravity (g) is substituted for acceleration (a). In other words, W = mg is a different form of So when the equation is solved for force, F = ma. The value of g in the formula is 9.8 m/s 2.

AN ASTRONAUT WITH A MASS OF 88 KG WEIGHS 863 N ON EARTH. AN ASTRONAUT WITH A MASS OF 88 KG WEIGHS 141 N ON THE MOON.

AN ASTRONAUT WITH A MASS OF 88 KG WEIGHS 863 N ON EARTH. AN ASTRONAUT WITH A MASS OF 88 KG WEIGHS 141 N ON THE MOON.

1. The velocity increases. 2. The velocity decreases. 3. The direction changes. 4. The motion does not change.

1. The velocity increases. 2. The velocity decreases. 3. The direction changes. 4. The motion does not change.

1. the crushing of the car's body 2. the air bag 3. the seatbelt 4. all of the above

1. the crushing of the car's body 2. the air bag 3. the seatbelt 4. all of the above

N N kg kg

N N kg kg

1. The two-cart chain would accelerate at half the rate of the single cart. 2. The two-cart chain would accelerate at twice the rate of the single cart. 3. The single cart would accelerate at half the rate of the two-cart chain. 4. They would accelerate at the same rate.

1. The two-cart chain would accelerate at half the rate of the single cart. 2. The two-cart chain would accelerate at twice the rate of the single cart. 3. The single cart would accelerate at half the rate of the two-cart chain. 4. They would accelerate at the same rate.

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 When one object exerts a force on a second object, the second object exerts and equal and opposite force on the fist object.  Video Clip (3:00)

 Example of the 3 rd law Hammer pushes on stake. Stake pushes on hammer. The hammer acts, the stake re-acts.

Definition: the product of an object's mass and its velocity SI Units : kilogram x meters per second. (kg x m/s) Keep in mind: An object has a large momentum if it has large mass and velocity is also large.

You can calculate momentum by multiplying an object's mass (in kilograms) and its velocity (in meters per second). Sometimes “P” is used for the word momentum

 Graph shows the speed and momentum of a 0.25-kilogram ball dropped from a bridge.  The graph shows the momentum of the ball from the time it was dropped until the time it hit the river flowing below the bridge.

 At what time did the ball have zero momentum? Time = 0 seconds

 Describe the ball at this point. The ball has zero momentum at this point. It’s NOT moving.

 At what time did the ball have the greatest momentum? Time = 2.5 seconds

 What was the highest momentum value? 6.5 kg m/s

 What was the ball’s speed after 1.5 seconds? 16 m/s

 In a closed system, the loss of momentum of one object equals the gain in momentum of another object—momentum is conserved.  See figures on page 376 of your text.  We will answer the following questions

Refer to Fig. A What is the mass of each train car? What happened to the momentum of the green car? What was the sum of the momentum of the cars before and after collision 30,000 kg The momentum was transferred from the blue car but NOT lost The sum was 450,000 before and after

Refer to Fig. B What is the mass of each train car? What happened to the momentum of the green car? What was the sum of the momentum of the cars before and after collision 30,000 kg The momentum was transferred from the blue and put it into motion The sum was 300,000 before and after

Refer to Fig. C What is the mass of each train car? What happened to the momentum of the green car? What was the sum of the momentum of the cars before and after collision 30,000 kg The momentum was transferred from the blue and put it into motion The sum was 300,000 before and after

Review In all cases, the momentum of each train car was conserved. It may have transferred from one car to another but it was NEVER lost. What type of systems were these examples?

 because they act on the same object  because they act on different objects  because they are not equal  because one of the forces is always zero

 because they act on the same object  because they act on different objects  because they are not equal  because one of the forces is always zero

massvelocity (kg x m/s)

 While driving down the road, a bug hits the windshield of a bus and goes “splat”! The firefly hit the bus and the bus hits the firefly.  Which of the two forces is greater: the force on the firefly or the force on the bus?

 For every action, there is an equal... (equal!).  The fact that the firefly splatters only means that with its smaller mass, it is less able to withstand the larger acceleration resulting from the interaction. Besides, fireflies have guts and bug guts have a tendency to be “splatterable”. Windshields don't have guts..

 The weakest universal force  Newton's law of universal gravitation states that every object in the universe attracts every other object.  IN OTHER WORDS: An attractive force that acts between any 2 masses.

 A Two masses, X and Y, attract each other.

 B The larger mass of X results in a larger gravitational force.

 C Increasing the distance between the masses significantly reduces the gravitational force.

 A center-directed force that continuously changes the direction of an object to make it move in a circle.

1. mass and distance 2. mass and air resistance 3. distance and air resistance 4. distance and velocity

1. mass and distance 2. mass and air resistance 3. distance and air resistance 4. distance and velocity

Let’s play…….

 The acceleration of an object is equal to the net force acting on it divided by the object's mass 2

 An object at rest tends to stay at rest and an object in motion tends to stay in motion (unless acted upon by an unbalanced force.) 1

 For every action, their is an equal and opposite reaction. 3

The End……………………………