Freefall
Which force pulls objects toward the Earth?
Gravity
What unit and symbol is used to measure force?
Newton (N)
Name one contact force and one non-contact force
Contact: Friction
Non-contact: Gravity
What device is used to measure a force?
A force meter or spring scale
What is a force?
A push or pull on an object
What happens when unbalanced forces act on a stationary object?
The object will start to move in the direction of the greater force.
Classify the following as contact or non-contact forces:
gravity, friction, air resistance.
Gravity -- non-contact
Friction -- contact
Air resistance -- contact
Is friction a helpful or harmful force?
Both. Helpful: prevents slipping
Harmful: causes wear (tyres)
What two things can happen to an object under balanced forces?
The object stays still or moves at a constant speed.
Explain why a ball eventually stops rolling on the ground.
Friction between the ball and the ground slows it down and stops it.
A skydiver opens a parachute. How does air resistance affect their motion?
Air resistance increases, slowing them down.
Why do astronauts float in space? Relate this to gravity.
They are in free fall due to low gravity, creating a feeling of weightlessness.
If a car is moving at constant speed, what can we say about the forces acting on it?
The driving force, friction and air resistance are balanced.
A person is pushing a box with 10N of force to the right, and friction is pushing back with 5N. What is the net force, and in which direction?
Net force = 5N to the right
Describe the forces acting on a book resting on a table.
Gravity pulls down, and the table pushes up with an equal force. The forces are balanced.
When dropped from a 2 metre height which object hits the ground first?
A crumpled up feather or a 1kg brick?
They both hit the ground at the same time as air resistance is negligible at this height.
Explain why objects weigh less on the Moon than on Earth.
The moon has less mass than Earth, so gravity is weaker there.
What are three ways to reduce friction? Give examples
Use lubricants (oil in engines), smooth surfaces (polished wood), or wheels (trolley on wheels vs dragging).
A tug-of-war team pulls with 500 N left and the other with 500 N right. What happens to the rope? Why?
The rope doesn't move; forces are balanced
When dropped from a 200 metre height, which item hits the ground first, a crumpled up piece of paper or a 1 kg brick? Why?
Air resistance is now a factor.
Predict what would happen if Earth's gravity were suddenly halved.
Everything would weigh half as much, and objects would fall more slowly
A spacecraft lands on a planet where everything falls more slowly than on Earth. What does this tell you about the planet's gravity?
The planet has a weaker gravity than Earth.
Explain why a car must accelerate in order to maintain speed when going up a hill.
Gravity pulls the car down the slope, and more force is needed to overcome it and move upward.
What would you measure and control when investigating how surface types affect friction?
Slide an object across different surfaces, measure force needed with a force meter. Control object weight and shape.
Name two instances when friction is good and bad in sports. One for each.
Good: traction in soccer
Bad: slows objects down (skating or cycling)