Newton’s Second & Third Laws

pgs. F16-F25Chapter 14 Lesson 2(simple machines is in another presentation)

1. balanced forces

• when forces cancel each other out they are balanced

• no change occurs from the force

2. unbalanced forces

• where one force acting on an object is greater than the other

• The force is partially cancelled.

3. action• when one object applies a force to another

object• what is done, something you do• kinetic energy

action

4. reaction

• the force that the object acted on returns• the result, what happens

reaction

5. Newton’s 3rd Law of Motion

• For every action, there is an equal but opposite reaction.

action reaction

How do these pictures demonstrate Newton’s 3rd Law of Motion?

So what is Newton’s 2nd Law?• Newton's first law tells us that a force is required to accelerate

an object. Newton's second law answers the question about how much force is required.

• F = ma (force = mass x acceleration) • You can tell how hard a moving object is going to hit by

knowing how big it is (how much mass it has) and how fast it is speeding up (its acceleration). For instance, if the pitcher throws the ball to the catcher, how hard it hits the catcher's glove depends on how much mass the ball has and whether it is speeding up or slowing down when it gets to the glove. You can make something hit harder either by making it bigger or by throwing it faster.

What affects acceleration?• forceTrue or False: The more force applied to an object

the farther the object goes. True. Right? Is this always true?

• What could cause this statement to be false?• mass (weight)What happens if the same amount of force is applied

to a heavy object? Will the object go as far?

Graphs: Understanding Acceleration

Calculating Acceleration We can determine how fast an object is moving by using this formula.• a = F ÷ m (acceleration = force ÷ mass)We can use this formula to determine how much force is being exerted on an object.• F = ma (force = mass x acceleration) • Force is measured in Newtons (N)

(Where do you think that came from?)

How fast are these objects moving? • a = F ÷ m or a = F/m (acceleration = force ÷ mass)• F = ma (force = mass x acceleration) • Acceleration can be measured in meters per second (m/s²)

Let’s try a couple problems! (you may use a calculator)

1. F = 2,000 N & M = 1,000 kg (2 m/s²)

2. F = 4,000 N & M = 2,356 kg (1.697 or 1.70 m/s²)

3. A = 1.5 m/s² & M = 2,000 kg (3,000 N)

4. A = 3.2 m/s² & M = 500 kg (1600 N)

SpeedS = D/T (speed = distance ÷ time)

1. Goldie Goldfish, a speed swimmer, loves to race around the park’s pond, which is 0.5 miles around. If she can swim 20 laps around the track in 2 hours, what is her average speed?

2. It takes Stu, a slimy slug, 20 minutes to travel from his favorite bush to the local trash can (a trip of 30 meters), how far can he travel in 1 hour (60 minutes)?

3. At exactly 2:00 pm, Speedy the Snail crawls onto a meter stick at the 10 cm mark. If he reaches the 65 cm mark at exactly 2:10 pm, what is his speed?

4. If it takes Leaping Louie 5 minutes to jump 3 blocks, how long will it take for him to jump 15 blocks?

http://www.science-class.net/7thGTPAP_Notes/Notes_Foce_Motion_GT.htm