Forces
What is a force?
A push or a pull acting on an object.
What is meant by “work done” in physics?
Work is done when a force moves an object through a distance.
What is a resistive force?
A force that opposes motion.
What is the formula for pressure?
P=A/F
A container is filled with water. Why is the pressure at the bottom greater than near the surface?
Because there is more water above the bottom, so the weight of the liquid creates greater pressure.
What happens when forces are balanced?
The object stays at rest or moves at a constant speed in a straight line.
What is the formula for calculating work done?
Work done = Force × Distance
Name two examples of resistive forces.
Friction and air resistance.
What happens to liquid pressure as depth increases?
Liquid pressure increases with depth.
A football is kicked and starts moving forward. Are the forces balanced or unbalanced? Why?
Unbalanced. A force was applied that caused the ball to accelerate.
What is the net force when forces are balanced?
Zero newtons (0 N).
A force of 10 N moves a box 5 m. How much work is done?
W=F×d=10×5=50J
In which direction does a resistive force act?
Opposite to the direction of motion.
What happens to pressure when the area increases but the force stays the same?
Pressure decreases.
A car engine provides 500 N forward. Resistive forces total 300 N backward. What is the net force and what happens to the car?
Net force = 200 N forward.
The car accelerates forward.
A book is resting on a table. Are the forces balanced or unbalanced? Explain briefly.
Balanced. The downward force of gravity is equal to the upward support force from the table.
A student pushes a wall but it does not move. How much work is done? Why?
0 J. No distance is moved, so no work is done.
Why does a sliding box eventually stop on the floor?
Because friction acts opposite to the motion and slows it down.
Why do sharp knives cut better than blunt knives?
Because they have a smaller area, so they create greater pressure.
Why does air pressure decrease at higher altitudes?
Because there is less air above, so there is less weight pressing down.
A car moves at a constant speed on a straight road. Are the forces balanced or unbalanced?
Balanced. The driving force equals the friction and air resistance, so the net force is zero.
. A 20 N force moves an object 3 m. Then the same force moves it another 2 m. What is the total work done?
Total distance = 5 m
W=20×5=100 JW=20×5=100J
A cyclist pedals with a forward force of 100 N. Air resistance and friction together apply 100 N backward. What happens to the cyclist’s motion?
The cyclist moves at constant speed because the forces are balanced.
A force of 200 N acts on an area of 4 m². Calculate the pressure.
P=F/A=200/4=50Pa
Why do parachutes increase air resistance?
They increase surface area, which increases air resistance and slows the falling object.