1. FORCE

2. NEWTON’S FORCES What is a force? –Push or pull exerted on an object –Vector (size and direction) –Variable: F Newton’s 3 Laws of Motion

3. An object at rest tends to stay at rest. An object in motion tends to stay in motion in a straight line unless acted upon by an external force. NEWTON’S FIRST LAW

4. NEWTON’S SECOND LAW

5. FORCE F = m a F : force (Newtons, N) m : mass (kilograms, kg) a : acceleration (m/s 2 )

6. NEWTON’S THIRD LAW For every action there is an equal and opposite reaction.

7. Types of Forces

8. WEIGHT W = m g W : weight (Newtons, N) m : mass (kilograms, kg) g : acceleration of gravity (9.8 m/s 2 )

9. Net Forces The total forces acting on an object Draw free-body diagram to show forces Ignore external forces Keep X and Y directions separate If the net force on an object is zero, the object is at equilibrium (at rest or constant velocity).  F=ma

10. Examples of Free-body Diagrams

11. The maximum speed that can be obtained by a falling objectmaximum speed The force of gravity is equally balanced by the air resistance force (drag). Constant speed, no acceleration

12. Measuring Effects of Air Resistance Materials –Meter stick –Paper –Stopwatch –Scissors Procedures –Drop a flat piece of paper 2 m. Measure the time for it to fall. –Crumple the piece of paper into a loose ball. –Measure time to fall in 2 m. –Crumple the piece of paper into a tighter ball. –Measure time to fall 2 m. –Use the scissors to design your own paper object. –Measure time to fall 2 m. TypeTime (s) Flat paper Loosely crumpled Tightly crumpled Your design What characteristic of the paper affected the falling time the most?

13. CH 4 HW (p113-115) 59.-9.8 N 60. 0.125m/s 2 61. 6,900 N 64. 250 kg 65. balloon, basketball, shot- put (b. reverse) 70. 250 N, bag does not hold 73. -14 m/s, 3185 N 80. Top to bottom: 45 N, 57 N, 93 N 82. 138 m 89. 9.8 m/s 2, 98 m/s, -49 N, 10 s

14. W = m g f =  F N F = ma  F=ma FNFN

15. Launching Force Project Objective –Apply the equations of motion and Newton’s Laws Materials –2-L bottle –Cardstock, tape, scissors, etc. Deadlines –Construct in-class by Thursday –Launch next Friday

16. Lego My Car Materials –Lego kits –Spring scales –Masses Procedures oUsing the Lego kit, build a simple car or truck. Be sure it is large enough to hold some small masses and a place to attach the spring scale. oPlace the car on a level surface. Attach the spring scale to it. oWith a constant velocity, pull the car along the ground with the spring scale. oRecord the value of the force. oChange the weight of the car by adding more masses. Repeat 3 times. oBased on your results, what is the relationship between weight and applied force?