Study sheet: Exploring Forces

📋 Course Outline

1. Force as Push or Pull
2. Effects of Force
3. Force and Interaction
4. Contact Forces and Friction
5. Non-Contact Forces
6. Gravity and Weight
7. Measuring Weight with Springs
8. Mass and Weight Compared
9. Buoyancy and Floating

📖 1. Force as Push or Pull

🔑 Key Concepts & Definitions

• Force : a push or pull on an object resulting from the object’s interaction with another object

💡 Memory Hook

A push or pull is the common basis of force.

📖 2. Effects of Force

★ Must-know

• A force may:
  • make an object move from rest
  • change the speed of an object
  • change the direction of motion of an object
  • change the shape of an object
  • cause some or all of these effects

Further detail

• Hitting a moving ball with a bat can change the direction of the ball, while pressing an inflated balloon can change its shape.

💡 Memory Hook

MSDS: Move, Speed, Direction, Shape.

📖 3. Force and Interaction

🔑 Key Concepts & Definitions

• Interaction : At least two objects must interact for a force to come into play.

★ Must-know

• The SI unit of force is the newton, whose symbol is N.

Further detail

📌 When two objects interact, each object experiences a force from the other, and both forces disappear when the interaction ceases.

💡 Memory Hook

Interaction between objects → force; ending interaction → no mutual force.

📖 4. Contact Forces and Friction

🔑 Key Concepts & Definitions

• Contact force : acts only when there is physical contact between the objects
• Muscular force : Muscular force is the force resulting from the action of muscles, which contract and elongate during activities such as walking, lifting, pushing, jumping, or stretching.
• Friction : the contact force that acts when an object moves or tries to move over another surface and opposes the direction of motion or attempted motion

📝 Essential Points

📌 Friction arises from irregularities in contacting surfaces that lock into one another, and it is greater on rough surfaces than on smooth surfaces.

💡 Memory Hook

Muscular force needs contact to act; friction opposes motion between contacting surfaces.

📖 5. Non-Contact Forces

🔑 Key Concepts & Definitions

• Non-contact force : can affect an object even when the objects are not physically touching
• Magnetic force : Magnetic force is the force exerted by a magnet on another magnet or on a magnetic material without physical contact.
• Electrostatic force : Electrostatic force is the force exerted by a charged body on another charged body or on an uncharged body.

📝 Essential Points

• When two objects are rubbed together, both objects become charged with opposite kinds of static charge, called positive and negative.

💡 Memory Hook

Like magnetic and electrostatic charges may attract or repel, whereas gravity only attracts.

📖 6. Gravity and Weight

🔑 Key Concepts & Definitions

• Gravitational force : the force with which the Earth attracts objects towards itself, and it is always attractive
• Weight : the force with which the Earth pulls an object towards itself

★ Must-know

• 🔄 During vertical motion under gravity, an object:
  1. moves upward while slowing down
  2. stops momentarily at the top
  3. moves downward with increasing speed

Further detail

• The SI unit of weight is the newton, written N.

💡 Memory Hook

Upward motion slows → topmost stop → downward motion speeds up.

📖 7. Measuring Weight with Springs

★ Must-know

• A spring balance measures weight because hanging an object stretches its spring, and the amount of stretching is read on a scale marked in newtons.

Further detail

• The illustrated spring balance has a range of 0 to 10 N and a smallest measurable division of 0.2 N.

📌 An object should not be heavier than the maximum value a spring balance can measure, otherwise the instrument may be damaged.

💡 Memory Hook

Hang object → spring stretches → read the newton scale.

📖 8. Mass and Weight Compared

★ Must-know

📌 Mass is the amount of matter in an object and remains the same everywhere, whereas weight is gravitational force and can vary from place to place or between planets.

• For a 1 kg object, the listed weights are:
  • 10 N on Earth
  • 1.6 N on the Moon
  • 3.8 N on Mars
  • 9 N on Venus
  • 25.4 N on Jupiter

Further detail

📌 Using kilograms to describe the mass of an object is scientifically correct, even though everyday speech often calls the mass of goods their weight.

💡 Memory Hook

Mass stays constant; weight changes with gravitational force.

📖 9. Buoyancy and Floating

🔑 Key Concepts & Definitions

• Buoyant force : the upward force applied by a liquid on an object placed in it

★ Must-know

📌 An object sinks when its gravitational force is greater than the buoyant force, and it floats when the two forces are equal.

• Archimedes’ Principle states that an object fully or partially immersed in a liquid experiences an upward force equal to the weight of the liquid it displaces.

Further detail

• Pumice can float on water because it is a light, porous rock containing air pockets and is less dense than water.

💡 Memory Hook

Gravity pulls down; buoyant force pushes up.

📊 Synthesis Tables

Contact and Non-Contact Forces

Force type	Examples	Main feature
Contact force	Muscular force, friction	Requires physical contact
Non-contact force	Magnetic, electrostatic, gravitational force	Acts without physical contact

Mass and Weight

Quantity	Meaning	Unit	Variation
Mass	Amount of matter	gram or kilogram	Remains the same
Weight	Gravitational force on an object	newton (N)	May vary with location