Force
“Force is an interaction between two objects, which comes in the form of a ____ or a ____.” (Weideman, 2024, "Definition of Force" section). "In a game of tug-of-war, opposing teams exert force on the rope to pull it toward their side" (Auburn University, n.d., "Introduction" section). A magnet exerts a force on magnetic objects, attracting or repelling them without direct contact. Using the given examples, fill in the blanks.
“Force is an interaction between two objects, which comes in the form of a push or a pull.” (Weideman, 2024, "Definition of Force" section). It is an interaction that can change an object's motion by making it speed up, slow down, or change direction (Bolles, 2024). Forces can act through direct contact, like friction, or at a distance, like gravity.
"Mass is a measure of the amount of matter in a substance or an object. The basic SI unit for mass is the _____" (Chemistry Libretexts, 2023, "Mass" section). This unit is often mistaken to represent weight, but actually represents mass. Weight is measured in newtons (N) because it is a force, while mass isn't as it's not a force, but rather, a constant (American Museum of Natural History). Using the given information, fill in the blank.
"Mass is a measure of the amount of matter in a substance or an object. The basic SI unit for mass is the kilogram (kg)" (Chemistry Libretexts, 2023, "Mass" section). Unlike weight, mass does not change based on location (American Museum of Natural History). For example, a 50 kg object on Earth has the same mass on the Moon.
Name one contact force. "A contact force is any force that occurs because of two objects making contact with each other" (Emigh et al., 2023, para. 1). Contact forces can be found everyday in actions like pushing a door, pulling a rope, or a book resting on a table (Emigh et al., 2023).
"Friction is a force that is around us all the time that opposes relative motion between surfaces in contact" (OpenStax, n.d., para. 1). It helps by allowing objects to grip surfaces, such as shoes preventing slipping or tires maintaining control on the road. Other main examples include tension, applied force, spring force, and buoyant force (Emigh et al., 2023).
What is buoyancy?
"Buoyant force is the upward force a fluid exerts on an object" (Khan Academy, 2016, para. 1). It determines whether an object will float or sink based on its density compared to the fluid (Khan Academy, 2016). Boats, for example, float because their shape displaces enough water to create a strong buoyant force.
"The SI unit of force is the ______" (National Physical Laboratory, n.d., para. 1). This unit is named after a famous scientist who formulated the laws of motion. It represents the amount of force needed to accelerate a 1 kg object by 1 m/s² (Davis, 2003).
"The SI unit of force is the Newton (N)" (National Physical Laboratory, n.d., para. 1). This unit is part of the International System of Units (SI), which is widely used in science, engineering, and most countries (National Institute of Standards and Technology, 2010). This unit was named after Sir Isaac Newton to commemorate his contributions to physics.
What is the difference between mass and weight?
"Mass is the total amount of matter, or 'stuff,' in an object. Weight is the force of gravity on an object" (American Museum of Natural History, 2016, para. 1). Mass is constant, but weight changes depending on the strength of the gravitational field (American Museum of Natural History, 2016). For example, you weigh less on the Moon than on Earth, but you will always have the same mass.
Name one action-at-a-distance force. "This force acts between distinct objects that are separated by some (non-vanishing) spatial distance, its influence is symmetric (in that any two massive objects influence each other), instantaneous and does not propagate continuously in space" (Berkovitz, 2007, "Action at a distance" section). It can be found in phenomena like Earth pulling objects downward or a magnet attracting metal from a distance (Khan Academy, 2022).
"Gravity, electric, and magnetic forces are non-contact forces that act over a distance, creating a field around an object" (Khan Academy, 2022, para. 1). These are all examples of action-at-a-distance forces, those being gravitational force and electromagnetic force. Other examples include strong nuclear force (the force holding atoms together), and weak nuclear force (the force responsible for radioactive decay) (University of Calgary, 2018).
"The density of water is roughly 1 gram per milliliter" (U.S. Geological Survey, n.d., "Overview" section). Explain why objects float or sink in water?
"An object that has a higher density than the liquid it's in will sink" (Science World, n.d., "Density, Sinking and Floating" section). A steel block sinks because it's dense, but a steel boat floats because it displaces more water (Benson, 2014). This principle is known as Archimedes’ Principle.
Newton's Second Law states that F = ____ x ____ (Khan, 2011, "About" section). This equation shows that the force acting on an object depends on its ____ and ____. It explains how objects respond to applied forces based on their inertia (Duston, 2023).
"Newton's second law of motion states that F = ma, or net force is equal to mass times acceleration" (Khan, 2011, "About" section). This means that a greater force is needed to move heavier objects or accelerate them faster (Neal, 2019). It explains why a small push can move a light object easily, but a stronger push is needed for a heavier object.
If a person weighs 600 N on Earth, would they weigh more or less when on the Moon?
"The gravitational attraction on the Moon is much less than it is here on Earth, and a person weighs less on the Moon" (Przyborski & Levy, 2004, "Gravity 101" section). Gravity on the Moon is about 1/6th of Earth's, so their weight would decrease proportionally (Barry & Bolles, 2025). Despite their weight going from 600 N to 100 N, their mass would remain unchanged.
How do magnets attract or repel objects without touching them?
"A magnet is surrounded by a magnetic field which pushes or pulls other magnets and things made of iron, nickel or cobalt that are located within it" (Victoria State Government, 2018, "Scientific View" section). The North and South poles of magnets attract each other, while like poles repel (University of Wisconsin-Madison, 2019). This is why a compass needle points north—it aligns with Earth’s magnetic field.
What is Pascal's Law?
"Pascal's law states that when there is an increase in pressure at any point in a confined fluid, there is an equal increase at every other point in the container" (Benson, 2021, para. 2). This principle allows hydraulic systems, such as car brakes and hydraulic lifts, to amplify force (Brain, 2000). By applying pressure to one part of a confined fluid, the force is distributed evenly, making it possible to lift heavy objects with minimal effort.
"Friction is a force that is around us all the time that opposes relative motion between surfaces in contact" (OpenStax, n.d., para. 1). True or false: according to Vern J. Ostdiek, friction can both help and hinder movement (Ostdiek & Bord, 2018). Using two examples, explain whether this is true or not.
"The force of friction is a fundamental concept that can either impede or facilitate movement" (Ostdiek & Bord, 2018, Chapter 2). It helps by allowing objects to grip surfaces, such as shoes preventing slipping or tires maintaining control on the road. However, it can also create resistance, making it harder for objects to move by slowing them down or causing wear over time (OpenStax, n.d.).
What is the difference between static and kinetic friction?
"Static friction occurs when two surfaces are not moving relative to one another, whereas kinetic friction occurs when two things move" (Unacademy, n.d., "Types of friction" section). For example, a heavy box may not move at first due to static friction, but once pushed harder, it starts sliding with kinetic friction. Engineers often design surfaces to reduce kinetic friction in machines.
Which of Newton’s laws explains why a seatbelt stops you from flying forward in a car crash? This law states that "a body at rest will remain at rest unless an outside force acts on it, and a body in motion at a constant velocity will remain in motion in a straight line unless acted upon by an outside force" (Hodanbosi et al., 1996, para. 1). It describes how your body continues moving forward until the seatbelt applies a force to stop you (Hodanbosi et al., 1996).
Newton's First Law (The Law of Inertia) explains this phenomenon (Hall, 2024). "Newton's First Law of Motion states that a body at rest will remain at rest unless an outside force acts on it, and a body in motion at a constant velocity will remain in motion in a straight line unless acted upon by an outside force" (Hodanbosi et al., 1996, para. 1). When a car abruptly stops, your body keeps moving forward, but the seatbelt applies a force to stop you.
What happens to gravitational force when two objects move farther apart?
"If the separation distance between two objects is doubled (increased by a factor of 2), then the force of gravitational attraction is decreased by a factor of 4 (2 raised to the second power)" (The Physics Classroom, n.d., "The UNIVERSAL Gravitation Equation" section). This is because gravity follows the inverse square law, meaning if the distance doubles, the gravitational force becomes four times weaker (Campbell, 2017). This is why planets farther from the Sun experience less gravitational pull, and why Pluto is drifting away.
Why do we use lubricants (like oil) in machines?
"lubricant is a substance (such as grease) capable of reducing friction, heat, and wear when introduced as a film between solid surfaces" (Merriam-Webster, n.d. para. 1). Over time friction can break down surfaces, leading to damage. Heat is also a byproduct of friction, which causes energy loss. (University of Colorado).