Force and Motion Full Unit All

• Learn to describe motion using speed and forces.

• Use Newton's laws: inertia and F=ma.

• Explain action-reaction pairs using Newton's Third Law.

• Investigate gravity, mass, weight, and energy of motion!

• Motion happens when an object changes position over time.

• To see motion, we use a fixed "reference point" or frame.

• A tree or building can be a steady reference frame.

• Is it moving? It's relative to your chosen reference frame!

Motion and Reference Frames

• Ever pushed a swing? That's a force – a push or a pull!

• Forces make things move, stop, speed up, slow down, or turn.

• Forces have power (strength in Newtons, N) and a direction.

• Cool diagrams use arrows to show a force's power and path!

What is Force?

​​Contact Forces

• ​Can act even if objects don't touch.

• ​​Like gravity pulling you down.

• ​Or magnets attracting or repelling.

​​Noncontact Forces

• ​Need objects to touch to act.

• ​​Like pushing a shopping cart.

• ​Or friction when a book slides.

​​Balanced Forces: Keeping it Steady!

• Forces are unequal or not directly opposite.

• Net force isn't zero – there's a winner!

• The object's motion changes (it accelerates!).

​​Unbalanced Forces: Making Moves!

• Equal forces push or pull opposite ways.

• Net force is zero – they cancel out!

• The object's motion stays the same.

• Speed shows how fast an object moves.

• It is the distance covered per unit of time.

• Formula: Speed = Distance / Time (e.g., 100m / 5s = 20 m/s).

• SI unit: m/s. Others: km/h, mph. Constant speed is a steady pace.

Zoom! How We Calculate Speed

​​Flash Speed!

• Overall speed for the entire journey.

• Calculated: Total Distance / Total Time.

• Example: 120km in 2 hrs is 60km/h.

​​Journey Speed!

• Your speed at one exact moment.

• Like a car's speedometer reading.

• It can change very quickly!

• Graphs plot distance (y-axis) against time (x-axis).

• Slope shows speed! Slope = Rise / Run (change in distance / change in time).

• Steeper slope? Faster speed! Horizontal line? Object is stationary (zero speed).

• A straight, positive slope means the object moves at a constant speed.

Interpreting Distance-Versus-Time Graphs

• Velocity is speed that also has a direction!

• It tells you how fast and which way something is going.

• Speed is '30 m/s'. Velocity is '30 m/s East' (it adds direction).

• Change speed or direction? Then the velocity changes too!

Velocity: It's Speed with Direction!

• Acceleration: how quickly an object's velocity changes.

• Speeding up is a common form of acceleration.

• Slowing down (deceleration) is also acceleration.

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

What is Acceleration?

• When objects collide, they exert forces on one another.

• Moving things have a special power: energy of motion (kinetic energy)!

• These forces can make things speed up, slow down, or change direction.

• In a collision, energy transfers, making objects move or stop.

Collisions: Force and Energy Transfer

• Objects at rest stay at rest.

• Objects in motion keep moving at constant velocity.

• This continues unless a net force acts on them.

• Objects resist changes in their state of motion.

Newton's First Law: The Law of Inertia

• Inertia: an object's tendency to resist motion changes.

• Objects at rest stay resting; objects in motion stay moving.

• This property is described by Newton's first law of motion.

• More mass means more inertia, so harder to move or stop.

Inertia: The Stubbornness of Objects!

• Acceleration (same direction as force) depends on net force and object's mass.

• ​The law's formula is: Force (F) = Mass (m) × Acceleration (a).

• More force = more acceleration. More mass = less acceleration (if force is same).

• Units: N (force), kg (mass), m/s² (accel). Also: a = F/m or m = F/a.

Newton's Second Law: Force, Mass, Acceleration

• Newton's third law: Every action has an equal, opposite reaction.

• If object A pushes B, object B pushes A back equally hard.

• These paired forces act on *different* objects, not the same one.

• So, these forces don't cancel out and can cause movement.

Newton's Third Law: Action-Reaction!

• Friction: a contact force opposing motion between rubbing surfaces.

• It always acts opposite to intended or actual movement.

• Factor 1: Surface type. Rougher surfaces cause more friction than smooth ones.

• Factor 2: Pressing force. More force (like a heavier box) creates more friction.

Understanding Friction - Factors Affecting It

• Static friction: Keeps things still. You beat it to move heavy furniture.

• Sliding friction: When surfaces rub! Like a book sliding across a table.

• Rolling friction: For wheels and balls. It's weaker than sliding friction.

• Fluid friction: In liquids or gases. Think air resistance for a skydiver.

Friction Fun: Stick, Slip, Roll, and Flow!

• Gravity is an invisible force pulling objects with mass together.

• On Earth, it pulls things down towards the planet's center.

• Newton showed it keeps planets and moons orbiting larger bodies.

• Free fall is when only gravity acts on a falling object.

Gravity - The Universal Force of Attraction

• Two main things decide how strong gravity is!

• More mass (like more stuff) means stronger gravity.

• The Sun is super massive, so its gravity pull is huge!

• The farther apart objects are, the weaker their gravity.

Gravity's Power: It's All About Mass & Distance!

​​Mass: The 'Stuff' Inside

• Measures the force of gravity on an object.

• Its SI unit is the newton (N).

• It changes based on the strength of gravity.

​​Weight: Gravity's Pull

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

• Its SI unit is the kilogram (kg).

• It stays the same, no matter your location!

• Kinetic energy is energy of motion. Moving things have it!

• It depends on two things: its mass and its speed.

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

• More speed means MUCH more energy! KE = 1/2 mv².

Concept 20: Kinetic Energy - The Energy of Motion

​Correction

• Constant motion needs no net force (Newton's 1st Law).

• Without air resistance, all objects fall at the same rate.

• Inertia is not a force; it resists motion changes.

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

​Misconception

• Motion always needs a force in its direction.

• Heavier objects always fall faster than lighter ones.

• Inertia is a force keeping objects moving/at rest.

• Action-reaction forces cancel, so no motion occurs.
  

• Motion is a position change relative to a reference frame.

• A force (push/pull) is needed to change motion (acceleration).

• Newton's 1st Law: Objects resist changes in their motion (inertia).

• Newton's 2nd Law: Net Force = Mass × Acceleration (F=ma).