Newton’s First Law
What must happen for a moving object to change its speed?
An unbalanced force must act on it.
Which object accelerates more: small mass or big mass (same force)?
Small mass
When you walk, what pushes you forward?
The ground
If the net force on an object is zero, what happens to its motion?
It stays the same
Mass = 2 kg, acceleration = 3 m/s². Force?
6 N
Why does a hockey puck slide farther on ice?
Less friction.
Calculate: F = 20 N, mass = 5 kg. Acceleration?
4 m/s².
A swimmer pushes water back. What does water do?
Pushes forward.
A box has 20 N pushing right and 10 N pushing left. What is the net force?
10 N right.
Force = 15 N, acceleration = 5 m/s². Mass?
3 Kg
If an object moves at the same speed and direction, what are the forces?
Balanced
If force increases and mass stays the same, what happens to acceleration?
It increases.
Why does a balloon zoom around when air escapes?
Air pushes backward; balloon moves forward.
If something moves at the same speed in a straight line, what does that mean about the forces?
They are balanced
If force increases, what happens to acceleration?
It increases
What word describes an object’s resistance to changes in motion?
Inertia
A cart accelerates at 3 m/s² when pushed with 15 N. Mass?
5 kg
A hammer hits a nail. What does the nail do?
Pushes back
A cart is speeding up. What does this tell you about the forces on it?
They are unbalanced.
Two objects accelerate differently under same force. What differs?
Mass
What happens to a sliding box if only friction acts?
It slows down
If mass doubles and force stays the same, what happens to acceleration?
It halves
Why don’t action–reaction forces cancel?
They act on different objects.
If a force pushes opposite the way an object is moving, what will happen to the object?
It slows down.
Force = 100 N, mass = 25 kg. Acceleration?
4 m/s².