Laws of Motion

Laws of Motion

Newton's first law of motion

• Newton's first law of motion states that every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force.

Force- a push or pull on an object. An object or a person can apply a force to another object or person.

• Contact force-a push or pull on one object by another that is touching it.

• Non contact forces- a force that once object can apply to another object without touching it. 

Forces

• Unbalanced Forces - Forces acting on an object that combine and 

  form a net force that is not zero.

• Balanced Forces-Forces acting on an object that combine and form a net force of zero

Inertia is the tendency of an object to resist a change in motion.

• A person is pedaling their bike and suddenly hits the front brakes and their body continues to move and they fly over the handle bars.

• A person is riding a jet ski in a straight line and suddenly turns the handles and their body continues moving in a straight line at the same speed as they are thrown from the jet ski.

The Net Force

• Net Force- the combination (sum) of all the forces acting on an object. The way forces combine, depends on the directions of the forces applied to an object.

• Combining forces in the same direction- when forces are applied to an object in the same direction, the net force is the sum of the individual forces.

Gravity

• Gravity- an attractive force that exists between all objects that have mass. Is a natural phenomenon by which all things with mass or energy—including planets, stars, galaxies, and even light—are brought toward one another. On Earth, gravity gives weight to physical objects, and the Moon's gravity causes the ocean tides.

• Mass- the amount of matter in an object.

• Matter- everything around you. Atoms and compounds are all made of very small parts of matter. Those atoms go on to build the things you see and touch every day. Matter is defined as anything that has mass and takes up space (it has volume).

• Weight- the gravitational force exerted on an object.

Law of Universal Gravitation. 

• This law states that all objects are attracted to each other by a gravitational force. The strength of the force depends on the mass of each object and the distance between them. 

  
  

• Gravitational Force and Mass- when the mass of one or both objects increases, the gravitational force between them also increases.

• Gravitational Force and Distance- the effect that distance has on gravity. The attraction between objects decreases as the distance between the objects increases.

Friction

• Friction- a force that resists the motion of two surface that are touching.

• Static Friction-prevents surfaces from sliding past each other up to a limit, the strength of static friction changes to match the applied force.

• Sliding Friction-opposes the motion of surfaces sliding past each other.

• Fluid Friction-friction between a surface and a fluid - any material, such as water or air that flows - is fluid friction. Fluid friction between a surface and air is air resistance.

Newton’s Second Law of Motion

• Newton’s Second Law of Motion- the acceleration of an object is equal to the net force acting on the object divided by the object’s mass

• Forces change an object's motion by changing its speed, direction or both speed and direction.

• When unbalanced forces act on an object at rest, the object moves in the direction of the net force.

• Unbalanced forces can change an object's velocity by changing its direction, can make an object accelerate by changing its speed, direction or both.

• Another name for a change in velocity over time is acceleration.

Circular Motion

• Circular motion is any motion in which an object is moving along in a curved path.

• Centripetal Force - in a circular motion, a force that acts perpendicular to the direction of motion, toward the center of the curve.

• Centripetal force is the force that keeps the object moving in a circular path. It does this by pulling an object toward the center of a circle.

The Motion of Satellites and Planets

• An example of a centripetal force is a satellite- an object in space that orbits a larger object. 

• Gravity is the centripetal force that keeps a satellite in orbit by changing its direction.

• The moon is a satellite of Earth, Earth gravity changes the moon’s direction

• The sun’s gravity changes the direction of its satellites, including Earth.

Newton’s third law of motion

• Newton’s third law of motion: when one object exerts a force on a second object, the second object exerts an equal force in the opposite direction on the first object. 

  
  

• For every action force there is a reaction force that is equal in strength but opposite in direction.

• Newton's first two law of motion describe the forces acting on a single object, while the third law describes the forces between two objects.

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Momentum

• Momentum is a measure of how hard it is to stop a moving object- It is the product of an object’s mass and velocity. An object’s momentum is in the same direction as it velocity. 

• Momentum is the product of mass and velocity, then force on an object equals its change in momentum.

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The Law of Conservation of Momentum-

• The Law of Conservation of Momentum-the total momentum of a group of objects stays the same unless outside forces act on the objects. 

  
  

• When objects collide and bounce off each other it is called an elastic collision.

• If objects collide and stick to each other, it is called an inelastic collision.

Force Pairs

• Force Pairs

  The forces described in Newton's Third Law depends on each other.

• A force pair is the forces two object apply to each other. They always act against each other; they act in opposite directions and are always the same strength.

• Each force acts on a different object; action and reaction.