Chapter 2 B Investigating Motion

Gravity is a force that pulls two objects together due to the attraction between their masses. It is a fundamental force of nature that exists between all objects with mass. Gravity is responsible for keeping the planets in orbit around the sun, causing objects to fall towards the Earth, and holding galaxies together. It is a universal force that acts at a distance, and its strength depends on the mass of the objects involved and the distance between them.

Weight is the measure of the force of gravity on an object. It is the downward force experienced by an object due to the gravitational pull of the Earth or any other celestial body. Weight is directly proportional to the mass of an object, meaning that the more massive an object is, the greater its weight will be. Weight is typically measured in units of force, such as pounds or newtons. Therefore, weight is the correct answer for the given question.

If you run at a speed of 5 mph for 3 hours, you would cover a distance of 15 miles. This can be calculated by multiplying the speed (5 mph) by the time (3 hours), which gives us 15 miles.

As you move farther away from Earth, the gravitational force exerted by Earth on you decreases. This is because gravity follows an inverse square law, which means that the force of gravity weakens with distance. Therefore, the statement that the farther away you get from Earth, the less you feel the effect of its gravity is true.

Gravity causes an object to accelerate as it approaches the earth. Gravity is the force of attraction between two objects with mass, and it pulls objects towards each other. As an object gets closer to the earth, the force of gravity increases, causing the object to accelerate towards the earth. This acceleration is due to the gravitational pull exerted by the earth on the object.

When you change direction while moving, it affects your velocity. Velocity is a vector quantity that includes both speed and direction. So, changing direction means altering the direction component of velocity. However, the speed component may remain the same. Therefore, changing direction affects velocity, but it may or may not affect speed, time, or gravity.

When you go to the moon, your weight decreases. This is because weight is determined by the force of gravity acting on an object, and the moon has a much weaker gravitational pull compared to Earth. Therefore, the force of gravity on your body is reduced, resulting in a decrease in weight.

When riding a skateboard, pushing your foot backwards against the floor generates a force in the opposite direction, according to Newton's third law of motion. This force propels the skateboard forward, causing it to move in the same direction as the applied force. Therefore, the correct answer is "moves forward."

Friction is the force that slows down a sled at the bottom of a hill. When the sled is moving downhill, friction acts in the opposite direction of its motion, causing it to slow down. Friction is the resistance between two surfaces in contact, and in this case, it occurs between the sled and the surface of the hill. As the sled slides down, the friction between the sled and the hill's surface converts some of its kinetic energy into heat, thereby slowing it down.

Fingerprints help you pick up a glass by increasing friction between your skin and the glass. The ridges and valleys in our fingerprints create more surface area for contact with the glass, increasing the friction between the two surfaces. This enhanced friction allows us to have a better grip on the glass and prevents it from slipping out of our hands.

Friction is a force that opposes the motion of an object. When an object is moving, friction acts in the opposite direction, causing the object to slow down. This is due to the interaction between the surfaces of the object and the surface it is moving on. Friction converts the kinetic energy of the moving object into heat energy, resulting in a decrease in the object's speed. Therefore, the correct answer is that friction slows down a moving object.

The weight of an object is determined by the force of gravity acting on it. Gravity is not constant everywhere, as it varies depending on the location and altitude. Therefore, when the force of gravity changes, the weight of an object also changes. This means that an object will weigh differently on the moon compared to on Earth, for example.

The opposing force to an action force is a reaction force. In Newton's third law of motion, it states that for every action, there is an equal and opposite reaction. This means that whenever a force is applied on an object, the object exerts an equal and opposite force back on the source of the original force. Therefore, the reaction force is the force that opposes the action force.

The speed of a car is calculated by dividing the distance traveled by the time taken. In this case, the car traveled 120 miles in 4 hours, so the speed is 120 miles divided by 4 hours, which equals 30 miles per hour.

Inertia refers to the tendency of an object to resist any change in its state of motion. If an object is at rest, it will stay at rest unless acted upon by an external force. Similarly, if an object is already in motion, it will continue moving at a constant velocity unless acted upon by an external force. Inertia is a fundamental property of matter and is related to its mass.

Air resistance is the correct answer because when an object moves through the atmosphere, the gas molecules in the air collide with the object's surface. These collisions create a force that opposes the motion of the object, causing it to slow down. This force is known as air resistance. Streamlining, on the other hand, refers to the design of objects in a way that reduces air resistance and allows for smoother movement through the air.

When a car is on cruise control and traveling at a constant speed, it means that there is no change in velocity. Acceleration is the rate of change of velocity, so if there is no change in velocity, the acceleration is zero. Therefore, the correct answer is zero.

Mass is the correct answer because it refers to the amount of matter in an object. It is a fundamental property of an object and is independent of its location or the force acting on it. Weight, on the other hand, is the force exerted on an object due to gravity and can vary depending on the object's location. Volume is the amount of space occupied by an object, while area refers to the measure of the surface of an object.

The statement suggests that objects with the same mass have an equal amount of gravitational attraction towards each other. This is because the force of gravity between two objects depends on their masses and the distance between them. If the masses are equal, the gravitational force between them will also be equal. Therefore, they attract each other equally.

The formula for speed is distance divided by time. This is because speed is defined as the distance traveled per unit of time. By dividing the distance by the time taken, we can determine how much distance is covered in a given amount of time, which gives us the speed.

The force of friction actually opposes the motion of an object. When an object is moving, the force of friction acts in the opposite direction to slow it down or stop it. Therefore, the statement that the force of friction moves in the same direction as the motion of an object is false.

Air resistance is the force that allows a parachute to fall safely to the ground. When a parachute is deployed, it creates a large surface area that interacts with the air molecules. As the parachute falls, the air resistance pushes against it, slowing down its descent. This counteracts the force of gravity, allowing the parachute and its wearer to descend at a controlled and safe speed. Without air resistance, the parachute would fall too quickly, potentially causing injury upon landing.

Friction is the force that resists the movement of one surface past another surface. When two surfaces are in contact, there are microscopic irregularities that interlock, causing resistance to motion. Friction can be influenced by factors such as the roughness of the surfaces, the force pressing the surfaces together, and the type of material involved. It acts in the opposite direction to the motion and can cause objects to slow down or come to a stop. Therefore, friction is the correct answer to the question.

Forces act in pairs means that for every action force, there is an equal and opposite reaction force. This is known as Newton's third law of motion. It states that whenever an object exerts a force on another object, the second object exerts an equal and opposite force back on the first object. This principle is observed in various everyday situations, such as pushing a wall and feeling the resistance pushing back. Therefore, the correct answer is true.

Objects of different masses pull on each other equally due to the force of gravity. However, according to Newton's second law of motion, the acceleration produced by a force is inversely proportional to the mass of the object. Therefore, the object with less mass will experience a greater acceleration and move towards the other object. This is why the correct answer is "moves toward the other object".

Force is the correct answer because it is the external influence that causes an object to move or stop. When a force is applied to an object, it can cause it to accelerate, meaning its speed and/or direction of motion changes. On the other hand, if the force acting on an object is removed or balanced by an equal and opposite force, the object will stop moving or remain at rest due to its inertia, which is the tendency of an object to resist changes in its state of motion.

If a planet has more gravity than Earth, it means that the planet has a greater gravitational force pulling objects towards it. Gravity is directly proportional to the mass of an object, which means that the greater the mass, the stronger the gravitational force. Therefore, if a planet has more gravity than Earth, it implies that the planet has more mass than Earth.

Acceleration is the rate at which an object's velocity changes over time. In the context of a plane, acceleration refers to how quickly the plane's velocity (speed and direction) changes. This can occur when the plane speeds up, slows down, or changes its direction. Therefore, acceleration is the correct answer as it accurately describes the rate at which a plane's velocity changes.

When a meteorite enters the Earth's atmosphere, it experiences a high amount of friction due to the air molecules present. This friction causes the meteorite to heat up rapidly, resulting in it burning up or vaporizing. The intense heat generated by the friction causes the meteorite to glow and produce a streak of light known as a meteor or shooting star. Therefore, the statement "A meteorite burns up as it enters our atmosphere because of friction" is true.

Adding oil, wax, or wheels can help reduce friction. Oil acts as a lubricant, creating a thin layer between surfaces, reducing the direct contact and friction. Wax also acts as a lubricant and can be applied to surfaces to reduce friction. Wheels, especially when made of materials with low friction coefficients like rubber or plastic, can reduce friction by rolling instead of sliding across surfaces. Therefore, adding oil, wax, or wheels can effectively reduce friction.

An object with rounded edges reduces the drag force acting on it, making it more streamlined. Having less surface area in the direction of motion also reduces the drag force, as there is less resistance to the object's movement. A large flat area in the front can create more drag, so it is not a characteristic of a streamlined object. Therefore, the correct answer is rounded edges and less surface area in the direction of motion.

Acceleration occurs when an object goes faster, slows down, or changes direction. This is because acceleration is the rate at which an object's velocity changes. When an object speeds up, its velocity increases, resulting in positive acceleration. Conversely, when an object slows down, its velocity decreases, resulting in negative acceleration or deceleration. Additionally, when an object changes direction, its velocity vector changes, leading to acceleration. However, when an object maintains a constant speed, there is no change in velocity, and therefore, no acceleration.