Forces Basics
What is a force?
A push or a pull.
What do we call an object resisting a change in motion?
Inertia
Newton’s 3rd Law says forces come in…
Equal and opposite pairs.
A book sits on a desk. What vertical forces appear?
Normal up, weight down.
A spring with k = 20 N/m is stretched 0.2 m. What is Fs?
4 N
Which force always opposes motion?
Friction
What kind of force is required to change an object’s motion?
An unbalanced force.
A ball pushes the ground with 50 N. How much does the ground push back?
50 N.
A box slides right. Which way is friction?
Left
A 6 N force stretches a spring with k = 30 N/m. How far?
0.2 m.
Which force is always perpendicular to a surface?
Normal force.
If the net force is zero, what can an object be doing?
At rest or moving at constant speed.
Why don’t action-reaction forces cancel out?
They act on different objects.
A cart accelerates right. Which force must be larger?
Rightward force.
A 12 N force pushes right; friction is 7 N left. What’s the net force?
5 N right.
What type of force acts without touching an object?
Field force (gravity).
What does “dynamic equilibrium” mean?
Object is moving at constant velocity.
A student pulls a wagon with 90 N. How hard does the wagon pull the student?
90 N in the opposite direction
Constant velocity requires what between applied force and friction?
They must be equal.
A 10 kg object has 5 N net force. What’s the acceleration?
0.5 m/s².
What do we call the combined total of all forces acting on an object?
Net force.
A sled is slowing down while sliding forward. What horizontal force must be present?
Friction backward.
True or False: Action–reaction forces act on the same object.
False
A spring stretches twice as far when the force is doubled. Which law explains this relationship?
Hookes Law
A spring stretches 0.25 m with 10 N. What is k?
40 N/m.