Types of Forces
Define a force in one sentence
A force is a push or a pull on an object.
What is a contact force? Give one simple classroom example.
A contact force is a push or pull when objects touch (e.g., pushing a book).
What is a noncontact force? Give one example.
A noncontact force acts without touching, e.g., gravity.
What is friction? Give a simple example.
Friction resists motion between touching surfaces, e.g., sliding on a floor slows you.
Give two everyday examples of pushes and two everyday examples of pulls.
Examples: push toothpaste from tube, push a door open; pull a chair out, pull a drawer open. (Any reasonable everyday examples accepted.)
Describe how a karate expert’s hand breaking boards is an example of a contact force (include mention of strength and direction).
Hand applies large force to boards; contact force from the hand is strong and directed to break boards.
Explain why a pencil falls to the floor when released using the term “noncontact force.”
Gravity pulls the pencil toward Earth even though nothing touches it.
Name and briefly define the three types of friction described in the text.
Static friction (prevents motion up to a limit), sliding friction (opposes motion while sliding), fluid friction (resistance from a fluid like air or water).
Explain in your own words why some forces act only when objects touch and other forces act without touching.
Crumpled paper has less surface area facing down, so less air resistance and falls faster.
Explain how tectonic plate movement is a result of contact forces and name one geological feature such forces can create.
Plates push against each other (contact); over time one plate may be pushed upward forming mountain ranges.
Name two noncontact forces mentioned in the text and give a short example of each from everyday life.
Examples: gravity — objects fall; magnetic force — magnets attract iron; electric force — static makes hair stand.
Explain why crumpled paper falls faster than flat paper, using the idea of fluid friction.
Crumpled paper has less surface area facing down, so less air resistance and falls faster.
A student lists “wind, gravity, magnetism, and friction.” Which of these are contact forces and which are noncontact forces? Explain briefly.
Wind is a fluid force often treated as a contact (air pushing surfaces) — contact; gravity and magnetism are noncontact; friction is a contact force. (Accept explanations.)
A box does not move when you push it lightly, but moves when you push harder. Explain this using static friction and contact forces.
Static friction matches applied force up to a limit; if push < static friction, box doesn't move; when applied force exceeds static friction, it moves
The text says an astronaut 350 km above Earth still has almost the same weight. Explain why gravity still acts at that distance (use a short, clear sentence).
Because Earth is very large; the relative change in distance is small, so gravitational force remains nearly the same.
Describe two causes of friction at the microscopic level according to the text.
Microscopic dips and bumps catch on each other; weak electrical charges on particles attract and resist sliding.
Describe an everyday situation that involves at least three different forces acting at once. Identify each force and whether it is contact or noncontact.
Example: Riding a bicycle — gravity (noncontact) pulls you down, friction (contact) between tires and road slows/stops, and applied force (contact) from your legs turns the pedals.
Design a short experiment (materials and steps) to measure how changing surface roughness affects the amount of force needed to start moving a small object across a table (include how you would record results).
Example experiment: use a small block, sandpaper of different grits, spring scale to pull block until it moves; record force to start movement for each surface; plot force vs roughness.
Compare and contrast electric force and magnetic force. Include one real-world example where each can be observed.
Electric force acts between charged objects (e.g., static electricity causing hair to stand); magnetic force acts between magnets and certain metals (e.g., fridge magnet). Both act at a distance; electric forces can attract/repel depending on charge, magnets have poles and attract certain materials.
Explain how lubricants (like soap or motor oil) reduce friction, and give one practical situation where reducing friction is helpful and one situation where increasing friction is helpful.
Lubricants separate surfaces and reduce microscopic contact and electrical attractions, lowering friction; helpful reducing friction: engine parts with oil; helpful increasing friction: shoe soles on ice or brake pads on wheels.