motion and forces

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Motion :

Motion When an object changes position over time from a starting point. Remember all particles are in motion no matter how tiny.

Speed :

Speed The rate at which an object is moving. The distance traveled and the time it takes to travel that distance. Expressed in km/ h

Average Speed :

Average Speed Average Speed = total distance total time

Velocity :

Velocity Direction Matters The speed of an object in a certain direction. Velocity changes as speed or direction changes

Acceleration :

Acceleration Acceleration is the rate at which velocity changes When you speed up, you change velocity because you change your speed. Acceleration = final velocity –starting velocity time it takes to change velocity Expressed in meters/second/ second

Graphing Acceleration :

Graphing Acceleration Time Velocity (m/s)

Energy of Motion :

Energy of Motion Kinetic Energy – the energy an object has while it is moving Potential Energy – the energy an object has before it moves

Kinetic Energy :

Kinetic Energy The energy of motion An object gets kinetic energy from its mass and velocity. Ek = ½ m v2 K.E. = ½ x mass (kg) x velocity (m/s/s) ²

Potential Energy :

Potential Energy Potential energy is the energy of POSITION. An object with potential energy has the potential to do work. Ep = mgh P.E. = mass x gravity (9.8 m/s2) x height

Forces :

Forces In science, a force is simply a push or a pull. All forces have both size and direction Forces are everywhere Scientists express force using a unit called a newton (N). All forces are exerted by one object on another object.

Net Force :

Net Force 20 N 15 N 10 N 25 N 20 N + 25 N = 45 N to the right 15 N - 10 N = 5 N to the right

Friction :

Friction A force that opposes motion Friction occurs because the surface of any object is rough The amount of friction between two objects depends on the roughness of their surfaces.

Static Friction :

Static Friction Also called “starting friction” The friction on an object before it starts moving

Kinetic Friction :

Kinetic Friction Friction against an object when it is MOVING.

Sliding Friction :

Sliding Friction The friction an object has when being pushed or pulled across a flat surface. PUSH FRICTION

Rolling Friction :

Rolling Friction The reduced friction when an object is placed on wheels or something round. PUSH FRICTION

Force and Friction :

Force and Friction

Ways to reduce friction :

Ways to reduce friction Lubricants – applied to surfaces to reduce the friction between them Ex: motor oil, wax, grease Switching from sliding friction to rolling friction Smoothing the surface of an object

So what is GRAVITY? :

So what is GRAVITY? Gravity is a force of attraction between objects that is due to their masses. Because all matter has mass, all matter experiences gravity The amount of attraction between objects depends on two things – the masses of the objects and the distance between them

GRAVITY :

GRAVITY Gravitational force is large between objects with large masses that are close together. Gravitational force is smaller between objects with smaller masses that are close together. An increase in distance reduces the gravitational force between two objects.

Gravity and Motion :

Gravity and Motion All objects fall with the same acceleration All objects accelerate towards earth at 9.8 meters per second per second Air resistance slows down acceleration Free fall occurs when there is no air resistance

Newton’s First Law of Motion :

Newton’s First Law of Motion An object at rest remains at rest and an object in motion remains in motion at a constant speed and in a straight line unless acted on by an unbalanced force. Also called the Law of Inertia An object that is not moving will not move until a force acts upon it. An object that is in motion will not change velocity (including stopping) until a force acts upon it.

Inertia :

Inertia The tendency of all objects to resist any change in motion. Mass is a measure of inertia. Ex: an object is harder to move when it has more mass

Newton’s Second Law of Motion :

Newton’s Second Law of Motion The acceleration of an object depends on the mass of the object and the amount of force applied As the force acting upon an object is increased, the acceleration of the object is increased. As the mass of an object is increased, the acceleration of the object is decreased. Force = mass x acceleration

Newton’s Third Law :

Newton’s Third Law For every action, there is an equal and opposite reaction. The size of the forces on the first object equals the size of the force on the second object. The direction of the force on the first object is opposite to the direction of the force on the second object. Forces always come in pairs - equal and opposite action-reaction force pairs.

In other words…

Centripetal Force :

Centripetal Force For objects in uniform circular motion, the net force and following acceleration is directed inwards. Circular motion requires a net inward or "centripetal" force.

Momentum :

Momentum Momentum can be defined as "mass in motion." All objects have mass; so if an object is moving, then it has momentum - it has its mass in motion. The amount of momentum which an object has is dependent upon two variables: how much stuff is moving and how fast the stuff is moving. Momentum depends upon the variables mass and velocity. Momentum (p) = mass x velocity

Find momentum… :

Find momentum… 1000-kg car moving east at 20 m/s. 20,000 kg*m/s, east 40-kg dog moving southward at 2 m/s. 80 kg*m/s south 