Chapter 3: Forces and Motion Flashcards
When do forces appear?
They appear when 2 objects interact with one another.
Contact force
When 2 objects touch.
Friction
Friction opposes motion.
It is the force that acts when 2 surfaces rub over one another.
Drag
The friction that acts on an object as it moves through a fluid (a liquid or a gas).
Air resistance
Friction acts on an object moving through air.
Solid friction (3)
-The resistance to motion is caused when 2 surfaces are in contact.
-It exists even when the surfaces are not moving against each other unless one or both surfaces are like ice and it offers almost no resistance to motion.
-They are said to have a very low coefficient of friction.
Uptrust
Is the upward push of liquid or gas.
What is a sideway force?
A sideways force causes an object to change direction.
Key points about forces (4)
-They can be represented by arrows which represent the direction of the force.
-Forces can make an object change speed.
-A forward force makes it speed up (accelerate) and a backward force causes it to slow down (deceleration).
-A force can change the direction in which an object is moving.
Resultant Forces (4)
-A body will remain at rest or will move at constant speed in a straight line unless acted upon by a resultant force.
-A resultant force will change the speed or direction of a body.
-A resultant will change the velocity of a body but as velocity is a vector,
-It is capable of changing both speed and direction simultaneously.
Balanced Forces (3)
Equal in size
Opposite in direction
The resultant is equal to 0.
Not Balanced Forces (2)
Resultant is nonzero
Not equal and acts in the same direction.
Mass vs Weight (3)
Mass
Measure in kilograms (kg)
Is how much matter an object is composed of
Mass can never change
Weight
Measured in Newtons (N)
Is the gravitational force that acts on the object
Weight can change
Statement about mass and weight
If two objects weigh the same, their mass is the same.
Why do Objects fall to the ground?
Because the force of weight acts on them.
Skydiver is jumping out of an aeroplane (2)
Weight force acts due to the earth’s gravitational force.
Unbalanced force due to a non-zero resultant (downwards).
The force of friction (air resistance) acts on the skydiver. (3)
-As the object accelerates (speed increases) air resistance slowly increases.
-Air resistance is caused by the force of friction with the colliding air particles.
-Unbalanced forces due to the non-zero resultant. (downwards).
Terminal Velocity (2)
-The object falls at a steady speed (due to the air resistance being equal to the weight-balanced forces)
-Forces are balanced when the resultant is zero due to being opposite and equal.
When the parachute is open (4)
-Air resistance increases due to the increase in surface area of the parachute.
-The object decelerates and then falls at a steady speed again.
-This is the second terminal velocity.
-Forces are balanced because it is 0 due to being equal and opposite.
Properties of centripetal force (4)
-The object moving in a circle is acted on by a force perpendicular to its motion.
-The force keeps the object moving in a circle and always acts towards the circle.
-Even if the object is moving at a constant speed, its velocity is changing as it is constantly changing direction.
-It is an unbalanced force due to velocity constantly changing meaning it is accelerating. And, The resultant force acting on the centre of the circle is a result of the perpendicular forces acting on the motion of the object.
A bigger force is needed if- (3)
-The object’s mass is bigger (speed and radius stay the same)
-The object’s speed is bigger (mass and radius stay the same)
-The radius of the circle is smaller (and the mass and speed stay the same).
What happens if the centripetal force disappears?
The object will move off a tangent not away from the center.
statement linking the mass, acceleration
The greater the mass of the object the smaller the acceleration is given by the particular force.
Law of Inertia (2)
Is the tendency of a body to resist a change in its motion.
A body continues to be in its state of rest or uniform motion unless acted upon by an unbalanced external force.
