Chapter 12 Forces and Motion
Force Force is a push or a pull.
A resting object to move Force A force can cause: A resting object to move Accelerate a moving object By changing the object's Speed Direction
Measuring Force
lbs - Pound N - Newton Measuring Force
Connecting Motion and Forces Force (newton, N): A push or pull one body exerts on another. Earth
Balanced Forces Balanced Forces: Forces on an object that are equal in size and opposite in direction.
Unbalanced Forces Unbalanced Forces: Forces on an object are not equal resulting in a Net Force. 5 N 3 N
Unbalanced Forces Unbalanced Forces: When an unbalanced force acts on an object, the object accelerates. 5 N 3 N
A Net Force on an object always changes the velocity of the object.
Balanced Forces Balanced Forces: When the forces on an object are balanced, the net force is zero and there is no change in the object's motion.
Friction Force that opposes the motion of objects that touch as they move past each other.
Static Friction A friction force that acts on objects that are not moving.
Sliding Friction A friction force that opposes the motion of an object as it slides over a surface.
Rolling Friction
Rolling Friction A friction force that acts on rolling objects, caused by the change in shape at the point of rolling contact.
Fluid Friction Air Resistance
Fluid Friction
A friction force that opposes the motion of an object through a fluid. Fluid Friction A friction force that opposes the motion of an object through a fluid.
Gravity Gravity: Every object in the universe exerts a force on every other object. This force is Gravity!!!
Gravity Gravity causes objects to accelerate downward, whereas air acts in the direction opposite to the motion and reduces acceleration.
Gravity Air Resistance
Projectile Motion
Projectile Motion
Projectile Motion Horizontal Component Vertical Component
Projectile Motion The combination of initial forward velocity and the downward vertical force of gravity causes the ball to follow a curved path.
Physical Science: 12-1 Worksheet: 12-1 Due:3/4/04
Force was required to keep an object moving at a constant speed. Aristotle
Object will move indefinitely Aristotle Object will move indefinitely if no force is applied.
Newton
Newton
Newton
Inertia Inertia (mass): The tendency of an object to resist any change in its motion. 25 kg 1kg
The more mass an object has, the greater its inertia.
stay in motion at a constant velocity unless a net force acts on it. Newton’s First Law The Law of Inertia An object in moving tends to stay in motion at a constant velocity and an object at rest remain at rest unless a net force acts on it.
Newton’s First Law
Newton’s Second Law of Motion The Law of Acceleration A net force acting on an object will accelerate that object in the direction of that force F a
FE FE - engine FNet FNet – net force FNet = FE - FF FF FF - friction Net Force Accelerates FNet FE FF FE - engine FF - friction FNet – net force FNet = FE - FF
FE=25N FN FN = FE - FF FN = 25N – 5N FN = 20N FF =5N Net Force Accelerates FN FE=25N FF =5N FN = FE - FF FN = 25N – 5N FN = 20N
Newton’s Second Law Acceleration Force = mass x acceleration F = ma
ma F = F F a m= m a F m a=
(Assume that there is no friction against the car.) Example #1 A car with a mass of 2000kg is parked on the side of the road. How much force is needed to accelerate the car at 3m/s²? (Assume that there is no friction against the car.)
Example #1 F
Given: m = 2000kg a = 3m/s² Find: F = ? Equation: F = ma F = (2000kg) x (3m/s²) F = 15,000N
Weight Weight: The measure of the force of gravity on an object.
Mass Mass: The amount of matter making up an object.
Weight Moon Earth Jupiter (16.7 lb) (100 lb) (254 lb)
Falling
{ Falling All objects fall at the same rate!! 9.8m/s² Acceleration due to Gravity!!! g 32ft/s² 22mph/s
W = mg Acceleration due to gravity. g Force due to gravity. W (weight) Falling Acceleration due to gravity. g Force due to gravity. W (weight) W = mg
Falling W W = Fair Terminal Velocity Fair
Homework: 12-2 Worksheet: 12-2 Due: 3/10/09
Math Practice Page: 367, 1-4 Due: 3/10/09 Homework: 12-3 Math Practice Page: 367, 1-4 Due: 3/10/09
A boy pushes forward a cart of groceries with a total mass of 40. 0 kg A boy pushes forward a cart of groceries with a total mass of 40.0 kg. What is the acceleration of the cart if the net force on the cart is 60.0 N? Given: Find: Equation: Solve:
What is the upward acceleration of a helicopter with a mass of 5000 kg if a force of 10,000 N acts on it in an upward direction? Given: Find: Equation: Solve:
Given: Find: Equation: Solve: An automobile with a mass of 1200 kg accelerates at a rate of 3.0 m/s2 in the forward direction. What is the net force acting on the automobile? (Hint: Solve the acceleration formula for force.) Given: Find: Equation: Solve:
Given: Find: Equation: Solve: A 25-N force accelerates a boy in a wheelchair at 0.5 m/s2 What is the mass of the boy and the wheelchair? (Hint: Solve Newton's second law for mass.) Given: Find: Equation: Solve:
Newton’s Third Law Action and Reaction When one object exerts a force on a second object, the second one exerts a force on the first that is equal in size and opposite in direction.
For every action there is an equal and Action and Reaction For every action there is an equal and opposite reaction.
Action - Reaction Pair
Rocket Propulsion Reaction Force Rocket Accelerates Action Force Escaping Gases
Momentum - Mass on the Move Momentum ( p unit:kg•m/s ) A property a moving object has because of mass and velocity.
v v
momentum = mass X velocity Momentum Equation momentum = mass X velocity p = m x v
Example: A car with a mass of 2000 kg is moving with a velocity of 40 m/s. What is its’ momentum? Given: m = 2000 kg v = 40 m/s Find: p = ? Equation: p = m x v Solve: p = 2000 kg x 40 m/s p = 80,000 kg•m/s
Conservation of Momentum The total momentum of a group of objects does not change unless outside forces act on the objects. The momentum before a collision is equal to the momentum after the collision.
Total Momentum Before = Total Momentum After
Total Momentum Before = Total Momentum After
Momentum
Homework: 12-3 Worksheet: 12-3 Due: 3/12/08
Universal Forces d
Electromagnetic Forces Electromagnetic forces are associated with charged particles.
Electric Forces
Magnetic Force Magnetic Poles
Unlike Poles (North-South) Attract!!!
Like Poles (North-North South-South) Repel!!!
Two forces that act in the nucleus to hold it together. Nuclear Force Two forces that act in the nucleus to hold it together. Strong Nuclear Force Weak Nuclear Force
Strong Nuclear Force Strongest Force Holds the nucleus together Short Range
Weak Nuclear Force Weaker than the Strong Force Short Range
Gravitational Forces
Any object with mass exerts a gravitation force. Long Range Gravitational Forces Any object with mass exerts a gravitation force. Long Range
Gravitational Forces
Tides
Tides
Circular Motion
Circular Motion V - Velocity Direction of Motion Centripetal Force (g) Acceleration
Sending up Satellites V = 29,000km/h (18,000mph)
Sending up Satellites Geostationary
Homework: 12-4 Worksheet: 12-4 Due: 3/13/09