Force Basics
What is a force?
A push or a pull
What is an applied force?
A push or pull put directly on an object
Which internal force stretches an object?
Tension
What does elasticity mean?
An object returns to its original shape
Which scientist explained action and reaction forces?
Sir Isaac Newton
Name two things a force can do to an object
Make it move, stop, speed up, slow down, or change direction
Which force opposes motion when two objects touch?
Friction
Which internal force squashes an object?
Compression
What does plasticity mean?
An object changes shape permanently
What does Newton’s Third Law say?
For every action, there is an equal and opposite reaction
What type of forces is gravity?
Non-contact force
A heavy box is harder to push on carpet than tile. Explain why.
Carpet creates more friction
A bridge holds many cars without collapsing. Which two internal forces are most important?
Tension and compression
A metal fork bends and stays bent. What property does this show?
Plasticity
When a swimmer pushes water backward, what is the reaction force?
Water pushes the swimmer forward
Are forces needed to change an object’s motion?
Yes
How does friction benefit us? Give one real-life example
Friction benefits us by helping us control movement and preventing slipping.
Real-life example:
When we walk, friction between our shoes and the ground prevents us from slipping and allows us to move forward safely.
Explain how scissors use shear force to cut paper.
Opposite forces slide layers past each other
Can the same material show both elasticity and plasticity? Explain.
Yes—depends on how much force is applied
A person pushes a wall but the wall doesn’t move. Are action and reaction forces still present?
Yes
A force is applied, but the object does not move. Give one possible reason.
Opposing forces are equal / friction is too strong
A magnet pulls a paper clip without touching it. What type of force is this and why?
Non-contact force; acts at a distance
When twisting a towel to remove water, which internal force is used and why does it work?
Torsion; twisting squeezes water out
Why do engineers care about elasticity and plasticity when building structures?
To prevent breaking or permanent damage
A rocket launches upward. Identify the action and reaction forces.
Action: gases pushed down / Reaction: rocket pushed up