Newtons Laws of Motion Forces change the motion

Newton’s Laws of Motion Forces change the motion of an object in very specific ways – Sir Isaac Newton (1642 -1727) was able to state the Laws that describe the effects of forces. 1

Newton’s 1 st Law of Motion Law of Inertia INERTIA is… the tendency for an object to resist its change in motion. It wants to stay where it is. No mom, I don’t want to go! First Law basically states that… An object in motion tends to stay in motion, while an object at rest tends to stay at rest until a force acts upon the object. 2

Newton’s 1 st Law of Motion - Continued The greater the mass of the object – the greater it’s inertia. Think about it like this… The book is sitting on the table is at rest. The book will stay there (remain at rest) until someone moves it (the outside force). 3

Newton’s 1 st Law of Motion - Continued Another example: If you were standing the same distance from a softball being hit or a baseball being hit which one would hurt more if it hit you? Which has more inertia? 4

Newton’s 2 nd Law of Motion Law of Acceleration Second Law basically states that…a force acting on an object causes the object to accelerate in the direction of that force. Force causes acceleration. Greater the mass – the greater the resistance to acceleration. 5

Newton’s 2 nd Law of Motion - Continued Let’s think about this one…if the soccer player kicks the soccer ball – which direction will the soccer ball go? Force causes acceleration of the object to accelerate in the direction of that force (the kicking of the ball). 6

Newton’s 2 nd Law of Motion - Continued Think about it like this… If the blue truck has a mass of 25, 000 kg and the red truck has a mass of 30, 000 kg which truck is going to take longer to speed up? The RED Truck – 30, 000 kg It goes back to the greater the mass – the greater the resistance to acceleration. 7

Newton’s 2 nd Law of Motion - Continued Newton’s 2 nd Law of Motion can be expressed in an equation: Force = Mass X Acceleration F = ma F m divide a multiply Force units = kg. m/s 2 OR Newton Mass units = kilograms (kg) Acceleration units = m/s 2 8

Newton’s 2 nd Law of Motion - Continued Problem: What force is exerted on a 1000 kg car accelerating at a speed of 15 m/s 2? Step 1 Read the problem. Draw a picture. 1000 kg 15 m/s 2 9

What force is exerted on a 1000 kg car accelerating at a speed of 15 m/s 2? Step 2 Write down what you know. What are you trying to find? 1000 kg 15 m/s 2 F= M= 1000 kg A= 15 m/s 2 10

What force is exerted on a 1000 kg car accelerating at a speed of 15 m/s 2? Step 3 Set up the formula. 1000 kg 15 m/s 2 Formula Substitute F= M= 1000 kg A= 15 m/s 2 Answer F = ma 11

What force is exerted on a 1000 kg car accelerating at a speed of 15 m/s 2? Step 4 Substitute the numbers. Solve. Box Answer with Units. 1000 kg 15 m/s 2 Formula F = 15, 000 N M = 1000 kg A = 15 m/s 2 F = ma Substitute F = 1000 kg x 15 m/s 2 Answer F = 15, 000 kg. m/s 2 OR F = 15, 000 N 12

Do problems 1 -3 in your notes. 13

Newton’s 2 nd Law of Motion - Continued The acceleration for any object moving under the sole influence of gravity. Any moving object being acted upon only by the force of gravity is said to be "in a state of free fall. " Characteristics of Free-Falling Objects: • do not encounter air resistance. • (on Earth) accelerate downwards at a rate of 9. 8 m/s 2. 14

Let’s Look at a Diagram Assuming that the position of a free-falling ball dropped from a position of rest is shown every 1 second, the velocity of the ball shown to increase as the time increases. What relationship do you notice about the distance per every 1 second? So…what type of acceleration does the ball have? Positive or Negative. 15

Remember the formula to find acceleration? a= Vf - V i t 16

Let’s Look at a Problem What is the velocity of a rubber ball dropped from a building roof after 5 seconds? Step 1 Step 2 Read the problem. Draw a picture. Write down what you know. What are you trying to find? Vf = Vi = 0 m/s t= 5 s a = 9. 8 m/s 2 17

What is the velocity of a rubber ball dripped from a building roof after 5 seconds? Step 3 Set up the formula. a= Step 4 Vf - V i t Substitute the numbers. Solve. Box Answer with Units. Formula a= Vf - Vi t Substitute Answer 49 m/s = Vf – 0 m/s 9. 8 m/s 2 = Vf – 0 m/s + 0 m/s = + 0 m/s 5 s 49 m/s = Vf 18

Do problems 4 & 5 in your notes. 19

Newton’s 3 rd Law of Motion Law of Action / Reaction Third Law basically states that…to every ACTION there is an equal and opposite REACTION. Action/Reaction forces act in PAIRS. 20

Newton’s 3 rd Law of Motion - Continued In this example, when the lady is walking, her feet push against the ground while the ground pushes against her feet. Thus action/reaction – pair is the feet and ground pushing off of one another. 21

Newton’s 3 rd Law of Motion - Continued Another example: Let’s think about this one…what are the pairs of forces that are acting against each other in order for the shuttle to launch? 22

MOMENTUM Property of a moving object because of its mass and velocity. An increase in mass or velocity causes an increase in momentum. 23

Momentum can be calculated with the following formula: Momentum = Mass X Velocity P = mv P m v Units for Momentum are kg. m/s 24

Problem: Find the momentum of an 7. 2 kg rock that is rolling down a hill with a velocity of 3. 0 m/sec. Step 1 Step 2 Read the problem. Draw a picture. Write down what you know. What are you trying to find? P = 21. 6 kg. m/s m = 7. 2 kg v = 3. 0 m/s Formula P = mv Step 3 Set up the formula. Step 4 Substitute the numbers. Solve. Box Answer with units. Substitute Answer P = 7. 2 kg x 3. 0 m/s P = 21. 6 kg. m/s Units, units! 25

Do problems 6 & 7 in your notes. 26

Law of Conservation of Momentum • In the absence of external forces applied to a system, the total momentum cannot change. • m 1 v 1 = m 2 v 2 27

Do problems 8 & 9 in your notes. 28