Study guide: 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

Mass and Weight