What is Newton’s Second Law of Motion
The acceleration of an object is :
-proportional to the resultant force on the object
-inversely proportional to the mass of the object
When does an object accelerate
If the resultant force of the object is in the same direction as the velocity
When does an object decelerate
The velocity of the object decreases if the resultant force is in the opposite direction to its velocity
What is inertia
The tendency of an object to stay at rest or continue in uniform motion
What is the formula for inertial mass
Force / acceleration
What is weight caused by
Gravitational force of attraction between you and the Earth.
What is weight
The weight of an object is the force acting on it due to gravity. Measured in Newtons (N)
What is mass
The mass of an object depends on the quantity of matter in it. Mass is measured in kilograms (kg)
What is the equation for weight, mass and gravitational field strength
Weight (N) = mass (kg) x gravitational field strength (N/kg)
What is the Earth’s gravitational field strength
About 9.8 N/kg
What happens if an object is released above the ground
If there are no other forces acting on the object it is said to be falling freely and the resultant force is its own weight downwards. It accelerates downwards at a constant acceleration of 9.8m/s ^2.
What effect does frictional force have on a falling object
-The acceleration of the object decreases because the frictional force increases as it speeds up so the resultant force decreases. Therfore its acceleration decreases.
- The object reaches a constant velocity when the frictional force on it is equal and opposite to its weight. This velocity is called terminal velocity. The resultant force is zero so its acceleration is 0
What is the stopping distance affected by
Thinking distance and braking distance
What is the thinking distance
The distance travelled by the vehicle in the time it takes the driver to react to a stimulus. Because the car keeps moving during the reaction time the thinking distance is equal to speed x reaction time. This shows that the thinking distance is proportional to speed.
What is the braking distance
The distance travelled by the vehicle during the time the braking force acts
What is the equation for stopping distance
Thinking distance + braking distance
What is the definition and formula for momentum?
Momentum is a measure of how difficult it is to stop a moving object. It is defined by the equation: p = m x v
Is momentum a scalar or a vector quantity? Why?
Momentum is a vector quantity. This is because it has both magnitude (size) and direction. Because velocity is a vector, momentum must also be a vector.
State the Law of Conservation of Momentum.
In a closed system, the total momentum before an event (like a collision or explosion) is equal to the total momentum after the event.
What is meant by a “closed system” in physics?
A closed system is a system where no external forces (like friction or air resistance) act on the objects involved.
If Trolley A hits stationary Trolley B and they stick together, why does their velocity decrease?
Because the total mass increases when they stick together. According to the conservation of momentum (π=πΓπ£), if the momentum stays the same but the mass increases, the velocity must decrease to compensate.
When a skateboarder jumps forward off a stationary board, why does the board shoot backwards?
This is an “explosion” event. Since the total momentum was zero at the start, the momentum after must also be zero. The forward momentum of the skater is cancelled out by the equal and opposite backward momentum of the skateboard.
State the Law of Conservation of Momentum as it applies to an explosion or collision.
In a closed system, the total momentum before an event is equal to the total momentum after the event.
Why is the momentum of one trolley often written as a negative number in calculations?
Momentum is a vector quantity, meaning direction matters. If two objects move in opposite directions (recoil), one direction is designated as positive (+) and the opposite as negative (-). This allows the total momentum to add up to zero.
