Learning Objectives

• Define motion and its reference frame.

• Describe forces and how they affect motion.

• Apply Newton's laws for motion, force, mass, acceleration.

• Calculate speed and use distance-time graphs.

• Motion is when an object's position changes from a reference frame.

• A reference frame is a place or object used for comparison.

• Fixed objects like trees or signs make good reference frames.

• Always state your reference frame to describe motion accurately.

What are Reference Frames and Motion?

• Relative motion: object's movement depends on your viewpoint (reference frame).

• ​An object can be moving or still, depending on the reference frame.

• On a beach towel, you're still. But you zoom fast relative to the Sun!

• Roller coaster: still in your seat, but speeding past the ground!

What's the Deal with Relative Motion?

• Force is a push or a pull on another object.

• It's measured by strength (newtons, N) and has a direction.

• Forces change motion: speed up, slow down, or change direction!

• Arrows show force: length for strength, point for direction.

Force: The Push and Pull Effect!

​​Contact Forces: Touchy-Feely!

• Objects do not need to touch.

• Examples: gravity, magnetism, electrical forces.

• Gravity pulls objects with mass together.

​​Noncontact Forces: Action at a Distance!

Types of Forces: Contact vs. Noncontact

• Objects must touch for these forces.

• Examples: pushing a box, friction.

• Friction opposes motion between surfaces.

​​Balanced Forces

• Forces are unequal or not opposite.

• Object's motion changes. Vroom!

• Net force is not zero. It moves!

​​Unbalanced Forces

Forces: Balanced or Unbalanced?

• Equal forces push/pull opposite ways.

• Object's motion stays the same.

• Net force is zero. No change!

• Speed: How fast an object moves, or distance covered per unit time.

• Formula: Speed = Distance / Time.

• Units: Measured in m/s (SI), km/h, or mph.

• Example: Skier covers 50m in 10s. Speed = 50m / 10s = 5 m/s.

Calculating Speed

​​Instantaneous Speed

• Total distance divided by total travel time.

• Formula: Total Distance / Total Time.

• Gives an overall speed for the journey.

​​Average Speed

Concept 7: Instantaneous and Average Speed

• Speed of an object at one specific instant.

• A car's speedometer shows this speed.

• It can change often during travel.

• A distance-time graph shows time (x-axis) and distance (y-axis).

• The line's slope tells you the speed. Slope = Rise / Run.

• Steeper slope means greater speed. A flat line means zero speed.

• Example: Rise 50m, Run 2s. Speed = 50m / 2s = 25 m/s.

Calculating Speed from Distance-Time Graphs

• Velocity is speed in a particular direction.

• It always includes both speed and direction.

• Change speed or direction, velocity changes too!

• Direction is vital for things like storms or planes.

Concept 9: Velocity

• Acceleration is how quickly velocity changes.

• It happens when an object speeds up.

• Slowing down is also acceleration (deceleration).

• Changing direction, even at constant speed, is acceleration.

Acceleration

• Moving objects have 'energy of motion' (kinetic energy).

• When objects collide, they can push each other with a force.

• This force can make a still object start to move.

• Collisions also transfer this energy of motion between objects.

Crash Course: Forces & Energy in Collisions!

• An object at rest will stay at rest.

• ​An object in motion stays moving at constant velocity.

• This happens unless a net (unbalanced) force acts on it.

• This resistance to motion change is called inertia.

Newton's First Law of Motion (Law of Inertia)

• Inertia is an object's resistance to changes in its state of motion.

• Newton's first law is also known as the law of inertia.

• More mass means more inertia, making it harder to change an object's motion.

• When a car stops, your body lurches forward due to inertia.

Inertia and Mass

• Acceleration changes with net force and an object's mass.

• The main formula is F = ma (Force = Mass × Acceleration).

• More force = more acceleration. More mass = less acceleration (like the sleighs!).

• Also a=F/m, m=F/a. Units: N (Force), kg (Mass), m/s² (Accel). 1N = 1kg·m/s².

Newton's Second Law of Motion

• Every action has an equal and opposite reaction force.

• Forces always occur in pairs, called action-reaction pairs.

• These forces act on different objects, so they don't cancel.

• Walking: Foot pushes ground (action), ground pushes foot (reaction).

Newton's Third Law of Motion

• Friction is a contact force when surfaces rub together.

• It acts opposite to the object's motion or attempted motion.

• Surface type matters: smooth surfaces have less friction.

• Pressing surfaces harder together increases the friction.

Friction and Its Factors

• Static Friction: The 'stay-put' force for objects at rest!

• Sliding Friction: The 'slow-down' hero when surfaces rub together.

• Rolling Friction: Wheels' best friend, making rolling easy!

• Fluid Friction: The 'drag' you feel moving through water or air.

Types of Friction

​​Gravity on Earth

• Gravity acts between all objects with mass.

• Any two objects with mass attract.

• Sun's gravity holds planets in orbit.

​​Law of Universal Gravitation

Concept 18: Gravity and the Law of Universal Gravitation

• A force pulling objects to Earth.

• Pulls them towards Earth's center.

• Makes objects fall down.

• Mass is key: Greater mass means stronger gravitational force.

• ​Example: The Sun's large mass creates very strong gravity.

• Distance also matters: Greater distance means weaker gravitational force.

• Gravity weakens a lot with distance (inverse square relationship).

Factors Affecting Gravitational Force

​​All About Mass

• Measures gravity's pull on an object.

• Its SI unit is the newton (N).

• Changes with gravity (W = m × g).

​​What is Weight?

Concept 20: Weight and Mass

• Measures the amount of 'stuff' in an object.

• Its SI unit is the kilogram (kg).

• Your mass stays the same everywhere!

• Kinetic energy is the energy an object has due to its motion.

• It depends on two things: the object's mass and its speed.

• More mass means more kinetic energy if speed stays the same.

• More speed means MUCH more kinetic energy (KE = 1/2 mv²)!

Kinetic Energy: Energy on the Move!

​Correction

• Constant motion needs no net force. Force *changes* motion.

• Objects fall at the same rate without air resistance.

• Inertia isn't a force. It resists motion changes.

• Action-reaction forces act on different objects, so they don't cancel.
  

​Misconception

Common Misconceptions

• Motion requires a force in its direction.

• Heavier objects always fall faster.

• Inertia is a force that keeps objects moving.

• Action-reaction forces cancel, preventing motion.
  

Summary

• Motion happens when things change position from a reference point. Groovy!

• Forces are pushes or pulls that make things speed up, slow down, or turn.

• Newton's awesome Laws show how forces and motion work together.

• Kinetic energy is motion energy! Gravity and friction are super important forces.