1 Forces Dynamics FORCEMAN
2 What causes things to move? Forces What is a force? A push or a pull that one body exerts on another.
3 Balanced No change in motion
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5 Unbalanced If the forces acting on a body are "unbalanced" this means that there is a "net" or "resultant" force. The body will do one of the following: 1. Speed Up 2. Slow Down 3. Change the Direction of its Motion In other words The Body will Accelerate
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7 Newtons SI unit of force is the Newton (N). Defined as the amount of force that when acting on a 1 kg object produces an acceleration of 1m/s 2. Therefore, 1N = 1 kg m s 2
8 Newton s First Law
9 Newton s First Law
10 Newton s First Law An object at rest stays at rest, and an object in motion stays in motion unless acted upon by a net external force. What do you mean by Net Force? Net means: Final Sum, so net external force is the sum of all the forces acting on the object.
11 Newton s First Law Newton s First Law is also called the Law of Inertia. Inertia is the tendency of an object to resist any change in its motion.
12 Why does the ladder continue to move? Inertia!
13 Why does the person continue to move? Inertia! Clip
14 Newton s Second Law The acceleration of an object is directly proportional to the net external force acting on the object and inversely proportional to the object s mass. F=ma Clip
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16 Newton's 2nd Law of Motion: Force = mass x acceleration F = (ma) Mass is in kg Acceleration is in m/s 2 Force is in kg x m/ s 2 (or N)
17 Force Problems: What force is needed to give an object with a mass of 25.0 kg an acceleration of 15.0 m/s 2? Formula Given: m = 25.0 kg a = 15.0 m/sec² F = ma Unknown: F =? F = (25 kg)(15 m/sec²) F = 375 kg m/sec² = 375 N
NewtoN s Third Law
34 Newton s Third Law of Motion to every action force there is an equal and opposite reaction force
35 Action- Reaction forces act on different objects
36 Review Newton s Laws Clip
18 Forces that oppose motion
19 Forces that oppose motion Friction Song 1 Friction Song 2
Forces that oppose motion -Air resistance is the force air exerts on a moving object
20 Friction What Causes Friction? Microscopic, electrostatic interactions between contacting surfaces
Friction 1. Static Friction 2. Sliding Friction 3. Rolling Friction
Types of Friction 21 Types of friction: 1. Static force required to overcome inertia of a stationary object
22 Static Friction (F S )
23 Types of Friction (cont.) 2. Sliding force required to keep an object sliding at a constant speed 3. Rolling force required to keep an object rolling at a To decrease friction, surfaces can be lubricated with a liquid such as oil. constant speed
FRICTION LAB
24 The amount of force CLIP required to overcome static friction is always greater than the force required to overcome sliding or rolling friction.
25 GRAVITY!! The force of gravity is an attractive force between objects. The amount of GRAVITATIONAL FORCE between objects depends upon their: 1- Masses (greater mass means more gravity) 2- Distance apart (greater distance means less gravity) *All objects fall toward the earth at the same rate of acceleration, regardless of their masses!
26 Calculating the Gravitational Force
27 Gravitation
28 Weightlessness Gravity in Space Moon Moon Hammer & Feather
29 Free fall and Terminal Velocity The opposing force of air resistance increases with speed. Objects accelerate towards the Earth until the force of gravity is cancelled or balanced by this air resistance. This is the highest speed an object can reach. Different objects have different terminal velocities.
30 Weight and Gravity W =m x g BECAUSE IT S A FORCE!
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32 Weight When the mass of an object and the acceleration due to gravity are known, the weight of an object can be calculated. Ex. Mass = 100kg Acc.= 9.81 m/s2 Weight = 981 N
33 Example Problem What is your weight if your mass 4.52 kilograms? Given: Unknown: m = 4.52 kg W =? g = a = 9.8 m/sec² Formula: W = mg W = (4.52kg)(9.8 m/sec²) W = 44.296 kg m/sec² = 44.296 N
37 Projectile Motion Projectiles follow a curved path because of the Earth s gravitational pull. They have 2 types of motion that are independent of each other: 1. Horizontal motion 2. Vertical motion
38 Projectile Motion Which will hit the ground first? A ball that is dropped straight down or a ball that is shot out horizontally? * An object launched horizontally will land on the ground at the same time as an object simply dropped from the same height!!!!
39 Another Example of Projectile Motion
40 Circular Motion An object moving in a circular motion at the same speed is accelerating toward the center because its direction is constantly changing. Centripetal acceleration is acceleration toward the center of a curved path. Roller Coaster Clip 'Centripetal' comes from the Latin word for 'center seeking' Centrifugal 'force' is really a function of the inertia of the object being pushed into a circle. It is not really a force at all, it is simply the tendency of an object to go in a straight line. only centripetal is the real force
41 Centripetal force is the force that causes a moving object to move in a curved path Circular Motion cont. Without a centripetal force, an object in motion continues along a straight-line path. With a centripetal force, an object in motion will be accelerated and change its direction.
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43 How do rollercoasters work!?! Amusement Park Forces