Forces, Movement & Changing Shape (Edexcel IGCSE Physics)

A scalar quantity is a quantity that has magnitude but not direction.

A vector quantity is a quantity that has both magnitude and direction.

True.

Mass is a scalar quantity as it has only magnitude.

False.

Distance is a scalar quantity.

300 N is a vector quantity. Newtons (N) are the unit of force, and force has both magnitude and direction; therefore, force is a vector quantity.

100 km due north is a vector quantity because it includes both a magnitude and a direction.

True

Energy is a scalar quantity. It has magnitude, but not direction.

Temperature is a scalar quantity.

False.

Weight is a force, so it is a vector quantity. Mass is a scalar quantity.

Speed is a scalar quantity with only magnitude. Velocity is a vector quantity with both magnitude and direction.

A resultant force is a single force that represents the combined effect of all forces acting on an object. It determines both the direction and the magnitude of the overall force experienced by the object.

The resultant force on the object is 3 N to the left.

The resultant force of the person in the chair is zero. The weight force and the reaction force are of equal magnitude and opposite in direction; therefore, the forces are balanced, so there is no resultant force.

If there is no resultant force acting on the car, then the forward and backward forces must be equal. Therefore, if the driving force is 2000 N, then the sum of the resistive forces must also be 2000 N.

True.

When the forces acting on an object are balanced, there is zero resultant force.

The equation for the resultant force is

Where:

• = resultant force, measured in newtons (N)

• = mass, measured in kilograms (kg)

• = acceleration, measured in metres per second squared (m/s²)

The symbol for resultant force is .

The units for resultant force are newtons (N).

The car is travelling forward, but the resultant force acts in the opposite direction to the motion of the car. This means that the car is decelerating or slowing down.

False.

Mass is a scalar quantity.

The S.I. unit kg stands for kilograms.

Weight is the effect of a gravitational field on an object with mass.

The symbol for gravitational field strength is .

False.

Mass is a measure of the quantity of matter in an object. Weight is a gravitational force on an object with mass.

False.

An object's mass is independent of gravitational field strength.

The stronger the gravitational field, the greater the weight force exerted on an object.

Weight is the force that causes objects to fall to the ground.

The equation for weight is

Where:

• = weight force, measured in newtons (N)

• = mass, measured in kilograms (kg)

• = gravitational field strength, measured in newtons per kilogram (N/kg)

True.

The mass of an object and the weight force acting on it are directly proportional. This means that doubling the mass will also double the weight force acting on the object.

The stopping distance of a car is the total distance travelled during the time it takes a car to stop in an emergency.

The equation used to calculate the stopping distance of a car is

The units for stopping distance are metres (m).

Thinking distance is the distance travelled in the time it takes the driver to react to an emergency and prepare to stop.

The two factors affecting thinking distance are:

• the speed of the car

• the reaction time of the driver

Reaction time is a measure of how much time passes between seeing something and reacting to it.

Three factors that can increase a driver's reaction time are:

• tiredness

• distractions

• intoxication

Braking distance is the distance travelled under the breaking force (of the car). This is the distance travelled by the car during the time the breaks are applied.

The four factors affecting stopping distance are:

• vehicle speed

• vehicle mass

• road conditions

• driver reaction time

Acceleration of free fall is the constant rate at which all objects fall in the absence of air resistance, typically denoted by the symbol and equal to approximately 10 m/s² near the surface of the Earth.

False.

In the presence of air resistance different objects fall at different accelerations and not at g. In most Physics questions we assume that air resistance is negligible.

True.

Acceleration of free fall remains constant regardless of an object's mass.

Terminal velocity is the fastest constant speed a falling object can reach. Terminal velocity is reached when the upward force of air resistance equals the downward force of weight, resulting in zero acceleration.

False.

Air resistance increases as the speed of a falling object increases.

Air resistance is the frictional force exerted by air particles on objects moving through air, which opposes the direction of motion.

Air resistance opposes the motion of objects falling through air, exerting an upward force that increases with the object's speed.

During free fall, weight acts downwards while air resistance acts upwards. As the speed of the object increases, air resistance increases until it equals the weight and terminal velocity is reached.

Terminal velocity occurs when the acceleration of a falling object becomes zero because the upward drag force equals the downward force of weight, resulting in a constant speed.

False.

The air resistance changes with speed during the fall of a skydiver.

The acceleration of free fall is equal to gravitational field strength. It is independent of the mass of the falling object.

Hooke’s law states that the extension of a spring is proportional to the applied force, up to the limit of proportionality.

False.

Hooke's Law states that the extension of a spring is directly proportional to the applied force.

The green arrow shows the linear portion of the graph. This is the section that obeys Hooke's law, where force and extension are directly proportional.

The green arrow shows the non-linear section of the graph where Hooke's law is not obeyed. Force and extension are no longer proportional.

The red cross represents the limit of proportionality. Beyond this point, force and extension are no longer directly proportional.

The elastic behaviour of a material is its ability to recover its original shape after the forces causing the deformation are removed.

True.

Deformation is a change to the original shape of an object that can be temporary or permanent.

False.

Inelastic deformation is a permanent change to an object's shape. Elastic deformation is a temporary change to an object's shape.